diff --git a/README.md b/README.md
index 8558e68..4d4a926 100644
--- a/README.md
+++ b/README.md
@@ -125,6 +125,10 @@ export const aUser = (overrides?: Partial<User>): User => {
 }
 ```
 
+### transformUnderscore (`boolean`, defaultValue: `true`)
+
+When disabled, underscores will be retained for type names when the case is changed. It has no effect if `typenames` is set to `keep`.
+
 ## Example of usage
 
 **codegen.yml**
diff --git a/src/index.ts b/src/index.ts
index 00146cd..c9dee22 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -20,21 +20,34 @@ type Options<T = TypeNode> = {
     enumsPrefix: string;
     currentType: T;
     customScalars?: ScalarMap;
+    transformUnderscore: boolean;
+};
+
+const convertName = (value: string, fn: (v: string) => string, transformUnderscore: boolean): string => {
+    if (transformUnderscore) {
+        return fn(value);
+    }
+
+    return value
+        .split('_')
+        .map((s) => fn(s))
+        .join('_');
 };
 
 const createNameConverter =
-    (convention: NamingConvention) =>
+    (convention: NamingConvention, transformUnderscore: boolean) =>
     (value: string, prefix = '') => {
         switch (convention) {
-            case 'upper-case#upperCase':
-                return `${prefix}${upperCase(value || '')}`;
+            case 'upper-case#upperCase': {
+                return `${prefix}${convertName(value, (s) => upperCase(s || ''), transformUnderscore)}`;
+            }
             case 'keep':
                 return `${prefix}${value}`;
             case 'pascal-case#pascalCase':
             // fallthrough
             default:
                 // default to pascal case in case of unknown values
-                return `${prefix}${pascalCase(value || '')}`;
+                return `${prefix}${convertName(value, (s) => pascalCase(s || ''), transformUnderscore)}`;
         }
     };
 
@@ -46,8 +59,8 @@ const toMockName = (typedName: string, casedName: string, prefix?: string) => {
     return `${a(firstWord, { articleOnly: true })}${casedName}`;
 };
 
-const updateTextCase = (str: string, enumValuesConvention: NamingConvention) => {
-    const convert = createNameConverter(enumValuesConvention);
+const updateTextCase = (str: string, enumValuesConvention: NamingConvention, transformUnderscore: boolean) => {
+    const convert = createNameConverter(enumValuesConvention, transformUnderscore);
 
     if (str.charAt(0) === '_') {
         return str.replace(
@@ -91,7 +104,7 @@ const getNamedType = (opts: Options<NamedTypeNode>): string | number | boolean =
 
     casual.seed(hashedString(opts.typeName + opts.fieldName));
     const name = opts.currentType.name.value;
-    const casedName = createNameConverter(opts.typenamesConvention)(name);
+    const casedName = createNameConverter(opts.typenamesConvention, opts.transformUnderscore)(name);
     switch (name) {
         case 'String':
             return `'${casual.word}'`;
@@ -109,11 +122,15 @@ const getNamedType = (opts: Options<NamedTypeNode>): string | number | boolean =
                 switch (foundType.type) {
                     case 'enum': {
                         // It's an enum
-                        const typenameConverter = createNameConverter(opts.typenamesConvention);
+                        const typenameConverter = createNameConverter(
+                            opts.typenamesConvention,
+                            opts.transformUnderscore,
+                        );
                         const value = foundType.values ? foundType.values[0] : '';
                         return `${typenameConverter(foundType.name, opts.enumsPrefix)}.${updateTextCase(
                             value,
                             opts.enumValuesConvention,
+                            opts.transformUnderscore,
                         )}`;
                     }
                     case 'union':
@@ -206,8 +223,9 @@ const getMockString = (
     addTypename = false,
     prefix,
     typesPrefix = '',
+    transformUnderscore: boolean,
 ) => {
-    const typenameConverter = createNameConverter(typenamesConvention);
+    const typenameConverter = createNameConverter(typenamesConvention, transformUnderscore);
     const casedName = typenameConverter(typeName);
     const casedNameWithPrefix = typenameConverter(typeName, typesPrefix);
     const typename = addTypename ? `\n        __typename: '${casedName}',` : '';
@@ -246,6 +264,7 @@ const getImportTypes = ({
     typesFile,
     typesPrefix,
     enumsPrefix,
+    transformUnderscore,
 }: {
     typenamesConvention: NamingConvention;
     definitions: any;
@@ -253,8 +272,9 @@ const getImportTypes = ({
     typesFile: string;
     typesPrefix: string;
     enumsPrefix: string;
+    transformUnderscore: boolean;
 }) => {
-    const typenameConverter = createNameConverter(typenamesConvention);
+    const typenameConverter = createNameConverter(typenamesConvention, transformUnderscore);
     const typeImports = typesPrefix?.endsWith('.')
         ? [typesPrefix.slice(0, -1)]
         : definitions
@@ -296,6 +316,7 @@ export interface TypescriptMocksPluginConfig {
     terminateCircularRelationships?: boolean;
     typesPrefix?: string;
     enumsPrefix?: string;
+    transformUnderscore?: boolean;
 }
 
 interface TypeItem {
@@ -316,6 +337,7 @@ export const plugin: PluginFunction<TypescriptMocksPluginConfig> = (schema, docu
 
     const enumValuesConvention = config.enumValues || 'pascal-case#pascalCase';
     const typenamesConvention = config.typenames || 'pascal-case#pascalCase';
+    const transformUnderscore = config.transformUnderscore ?? true;
     // List of types that are enums
     const types: TypeItem[] = [];
     const visitor: VisitorType = {
@@ -357,6 +379,7 @@ export const plugin: PluginFunction<TypescriptMocksPluginConfig> = (schema, docu
                         enumsPrefix: config.enumsPrefix,
                         currentType: node.type,
                         customScalars: config.scalars,
+                        transformUnderscore,
                     });
 
                     return `        ${fieldName}: overrides && overrides.hasOwnProperty('${fieldName}') ? overrides.${fieldName}! : ${value},`;
@@ -384,6 +407,7 @@ export const plugin: PluginFunction<TypescriptMocksPluginConfig> = (schema, docu
                                       enumsPrefix: config.enumsPrefix,
                                       currentType: field.type,
                                       customScalars: config.scalars,
+                                      transformUnderscore,
                                   });
 
                                   return `        ${field.name.value}: overrides && overrides.hasOwnProperty('${field.name.value}') ? overrides.${field.name.value}! : ${value},`;
@@ -399,6 +423,7 @@ export const plugin: PluginFunction<TypescriptMocksPluginConfig> = (schema, docu
                         false,
                         config.prefix,
                         config.typesPrefix,
+                        transformUnderscore,
                     );
                 },
             };
@@ -421,6 +446,7 @@ export const plugin: PluginFunction<TypescriptMocksPluginConfig> = (schema, docu
                         !!config.addTypename,
                         config.prefix,
                         config.typesPrefix,
+                        transformUnderscore,
                     );
                 },
             };
@@ -441,6 +467,7 @@ export const plugin: PluginFunction<TypescriptMocksPluginConfig> = (schema, docu
                         !!config.addTypename,
                         config.prefix,
                         config.typesPrefix,
+                        transformUnderscore,
                     );
                 },
             };
@@ -467,6 +494,7 @@ export const plugin: PluginFunction<TypescriptMocksPluginConfig> = (schema, docu
         typesFile,
         typesPrefix: config.typesPrefix,
         enumsPrefix: config.enumsPrefix,
+        transformUnderscore: transformUnderscore,
     });
     // List of function that will generate the mock.
     // We generate it after having visited because we need to distinct types from enums
diff --git a/tests/__snapshots__/typescript-mock-data.spec.ts.snap b/tests/__snapshots__/typescript-mock-data.spec.ts.snap
index c4dda14..3a09665 100644
--- a/tests/__snapshots__/typescript-mock-data.spec.ts.snap
+++ b/tests/__snapshots__/typescript-mock-data.spec.ts.snap
@@ -27,9 +27,16 @@ export const mockMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const mockPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const mockQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : mockUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : mockPrefixedResponse(),
     };
 };
 
@@ -91,9 +98,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -130,7 +144,7 @@ export const aWithAvatar = (overrides?: Partial<WithAvatar>): WithAvatar => {
 
 exports[`should add enumsPrefix to imports 1`] = `
 "/* eslint-disable @typescript-eslint/no-use-before-define,@typescript-eslint/no-unused-vars,no-prototype-builtins */
-import { AbcType, Avatar, CamelCaseThing, Mutation, Query, UpdateUserInput, User, WithAvatar, Api } from './types/graphql';
+import { AbcType, Avatar, CamelCaseThing, Mutation, PrefixedResponse, Query, UpdateUserInput, User, WithAvatar, Api } from './types/graphql';
 
 export const anAbcType = (overrides?: Partial<AbcType>): AbcType => {
     return {
@@ -157,9 +171,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -223,9 +244,16 @@ export const aMutation = (overrides?: Partial<Api.Mutation>): Api.Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<Api.PrefixedResponse>): Api.PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Api.Query>): Api.Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -287,9 +315,16 @@ export const aMutation = (overrides?: Partial<Api.Mutation>): Api.Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<Api.PrefixedResponse>): Api.PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Api.Query>): Api.Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -353,9 +388,16 @@ export const aMutation = (overrides?: Partial<Api.Mutation>): Api.Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<Api.PrefixedResponse>): Api.PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Api.Query>): Api.Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -417,9 +459,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -481,9 +530,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -545,9 +601,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -609,9 +672,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -673,9 +743,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -737,9 +814,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -776,7 +860,7 @@ export const aWithAvatar = (overrides?: Partial<WithAvatar>): WithAvatar => {
 
 exports[`should generate mock data functions with external types file import 1`] = `
 "/* eslint-disable @typescript-eslint/no-use-before-define,@typescript-eslint/no-unused-vars,no-prototype-builtins */
-import { AbcType, Avatar, CamelCaseThing, Mutation, Query, UpdateUserInput, User, WithAvatar, AbcStatus, Status } from './types/graphql';
+import { AbcType, Avatar, CamelCaseThing, Mutation, PrefixedResponse, Query, UpdateUserInput, User, WithAvatar, AbcStatus, Status } from './types/graphql';
 
 export const anAbcType = (overrides?: Partial<AbcType>): AbcType => {
     return {
@@ -803,9 +887,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -867,9 +958,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -931,9 +1029,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -995,9 +1100,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -1059,9 +1171,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -1098,7 +1217,7 @@ export const aWithAvatar = (overrides?: Partial<WithAvatar>): WithAvatar => {
 
 exports[`should generate mock data with PascalCase types and enums by default 1`] = `
 "/* eslint-disable @typescript-eslint/no-use-before-define,@typescript-eslint/no-unused-vars,no-prototype-builtins */
-import { AbcType, Avatar, CamelCaseThing, Mutation, Query, UpdateUserInput, User, WithAvatar, AbcStatus, Status } from './types/graphql';
+import { AbcType, Avatar, CamelCaseThing, Mutation, PrefixedResponse, Query, UpdateUserInput, User, WithAvatar, AbcStatus, Status } from './types/graphql';
 
 export const anAbcType = (overrides?: Partial<AbcType>): AbcType => {
     return {
@@ -1125,9 +1244,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -1189,9 +1315,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -1253,9 +1386,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixed_Response = (overrides?: Partial<Prefixed_Response>): Prefixed_Response => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixed_Response(),
     };
 };
 
@@ -1321,10 +1461,18 @@ export const aMutation = (overrides?: Partial<Mutation>): { __typename: 'Mutatio
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): { __typename: 'PrefixedResponse' } & PrefixedResponse => {
+    return {
+        __typename: 'PrefixedResponse',
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): { __typename: 'Query' } & Query => {
     return {
         __typename: 'Query',
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -1388,9 +1536,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -1452,9 +1607,16 @@ export const aMUTATION = (overrides?: Partial<MUTATION>): MUTATION => {
     };
 };
 
+export const aPREFIXED_RESPONSE = (overrides?: Partial<PREFIXED_RESPONSE>): PREFIXED_RESPONSE => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQUERY = (overrides?: Partial<QUERY>): QUERY => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUSER(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPREFIXED_RESPONSE(),
     };
 };
 
@@ -1491,7 +1653,7 @@ export const aWITHAVATAR = (overrides?: Partial<WITHAVATAR>): WITHAVATAR => {
 
 exports[`should generate mock data with upperCase types and imports if typenames is "upper-case#upperCase" 1`] = `
 "/* eslint-disable @typescript-eslint/no-use-before-define,@typescript-eslint/no-unused-vars,no-prototype-builtins */
-import { ABCTYPE, AVATAR, CAMELCASETHING, MUTATION, QUERY, UPDATEUSERINPUT, USER, WITHAVATAR, ABCSTATUS, STATUS } from './types/graphql';
+import { ABCTYPE, AVATAR, CAMELCASETHING, MUTATION, PREFIXED_RESPONSE, QUERY, UPDATEUSERINPUT, USER, WITHAVATAR, ABCSTATUS, STATUS } from './types/graphql';
 
 export const anABCTYPE = (overrides?: Partial<ABCTYPE>): ABCTYPE => {
     return {
@@ -1518,9 +1680,16 @@ export const aMUTATION = (overrides?: Partial<MUTATION>): MUTATION => {
     };
 };
 
+export const aPREFIXED_RESPONSE = (overrides?: Partial<PREFIXED_RESPONSE>): PREFIXED_RESPONSE => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQUERY = (overrides?: Partial<QUERY>): QUERY => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUSER(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPREFIXED_RESPONSE(),
     };
 };
 
@@ -1557,7 +1726,7 @@ export const aWITHAVATAR = (overrides?: Partial<WITHAVATAR>): WITHAVATAR => {
 
 exports[`should not merge imports into one if enumsPrefix does not contain dots 1`] = `
 "/* eslint-disable @typescript-eslint/no-use-before-define,@typescript-eslint/no-unused-vars,no-prototype-builtins */
-import { AbcType, Avatar, CamelCaseThing, Mutation, Query, UpdateUserInput, User, WithAvatar, ApiAbcStatus, ApiStatus } from './types/graphql';
+import { AbcType, Avatar, CamelCaseThing, Mutation, PrefixedResponse, Query, UpdateUserInput, User, WithAvatar, ApiAbcStatus, ApiStatus } from './types/graphql';
 
 export const anAbcType = (overrides?: Partial<AbcType>): AbcType => {
     return {
@@ -1584,9 +1753,16 @@ export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>): PrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>): Query => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -1623,7 +1799,7 @@ export const aWithAvatar = (overrides?: Partial<WithAvatar>): WithAvatar => {
 
 exports[`should not merge imports into one if typesPrefix does not contain dots 1`] = `
 "/* eslint-disable @typescript-eslint/no-use-before-define,@typescript-eslint/no-unused-vars,no-prototype-builtins */
-import { ApiAbcType, ApiAvatar, ApiCamelCaseThing, ApiMutation, ApiQuery, ApiUpdateUserInput, ApiUser, ApiWithAvatar, AbcStatus, Status } from './types/graphql';
+import { ApiAbcType, ApiAvatar, ApiCamelCaseThing, ApiMutation, ApiPrefixedResponse, ApiQuery, ApiUpdateUserInput, ApiUser, ApiWithAvatar, AbcStatus, Status } from './types/graphql';
 
 export const anAbcType = (overrides?: Partial<ApiAbcType>): ApiAbcType => {
     return {
@@ -1650,9 +1826,16 @@ export const aMutation = (overrides?: Partial<ApiMutation>): ApiMutation => {
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<ApiPrefixedResponse>): ApiPrefixedResponse => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<ApiQuery>): ApiQuery => {
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixedResponse(),
     };
 };
 
@@ -1687,6 +1870,79 @@ export const aWithAvatar = (overrides?: Partial<ApiWithAvatar>): ApiWithAvatar =
 "
 `;
 
+exports[`should preserve underscores if transformUnderscore is false 1`] = `
+"/* eslint-disable @typescript-eslint/no-use-before-define,@typescript-eslint/no-unused-vars,no-prototype-builtins */
+import { AbcType, Avatar, CamelCaseThing, Mutation, Prefixed_Response, Query, UpdateUserInput, User, WithAvatar, AbcStatus, Status } from './types/graphql';
+
+export const anAbcType = (overrides?: Partial<AbcType>): AbcType => {
+    return {
+        abc: overrides && overrides.hasOwnProperty('abc') ? overrides.abc! : 'sit',
+    };
+};
+
+export const anAvatar = (overrides?: Partial<Avatar>): Avatar => {
+    return {
+        id: overrides && overrides.hasOwnProperty('id') ? overrides.id! : '0550ff93-dd31-49b4-8c38-ff1cb68bdc38',
+        url: overrides && overrides.hasOwnProperty('url') ? overrides.url! : 'aliquid',
+    };
+};
+
+export const aCamelCaseThing = (overrides?: Partial<CamelCaseThing>): CamelCaseThing => {
+    return {
+        id: overrides && overrides.hasOwnProperty('id') ? overrides.id! : '345b9cf9-00fa-4974-800f-aeee5ee7fd42',
+    };
+};
+
+export const aMutation = (overrides?: Partial<Mutation>): Mutation => {
+    return {
+        updateUser: overrides && overrides.hasOwnProperty('updateUser') ? overrides.updateUser! : aUser(),
+    };
+};
+
+export const aPrefixed_Response = (overrides?: Partial<Prefixed_Response>): Prefixed_Response => {
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
+export const aQuery = (overrides?: Partial<Query>): Query => {
+    return {
+        user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : aUser(),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : aPrefixed_Response(),
+    };
+};
+
+export const anUpdateUserInput = (overrides?: Partial<UpdateUserInput>): UpdateUserInput => {
+    return {
+        id: overrides && overrides.hasOwnProperty('id') ? overrides.id! : '1d6a9360-c92b-4660-8e5f-04155047bddc',
+        login: overrides && overrides.hasOwnProperty('login') ? overrides.login! : 'qui',
+        avatar: overrides && overrides.hasOwnProperty('avatar') ? overrides.avatar! : anAvatar(),
+    };
+};
+
+export const aUser = (overrides?: Partial<User>): User => {
+    return {
+        id: overrides && overrides.hasOwnProperty('id') ? overrides.id! : 'a5756f00-41a6-422a-8a7d-d13ee6a63750',
+        creationDate: overrides && overrides.hasOwnProperty('creationDate') ? overrides.creationDate! : '1970-01-09T16:33:21.532Z',
+        login: overrides && overrides.hasOwnProperty('login') ? overrides.login! : 'libero',
+        avatar: overrides && overrides.hasOwnProperty('avatar') ? overrides.avatar! : anAvatar(),
+        status: overrides && overrides.hasOwnProperty('status') ? overrides.status! : Status.Online,
+        customStatus: overrides && overrides.hasOwnProperty('customStatus') ? overrides.customStatus! : AbcStatus.HasXyzStatus,
+        scalarValue: overrides && overrides.hasOwnProperty('scalarValue') ? overrides.scalarValue! : 'neque',
+        camelCaseThing: overrides && overrides.hasOwnProperty('camelCaseThing') ? overrides.camelCaseThing! : aCamelCaseThing(),
+        unionThing: overrides && overrides.hasOwnProperty('unionThing') ? overrides.unionThing! : anAvatar(),
+    };
+};
+
+export const aWithAvatar = (overrides?: Partial<WithAvatar>): WithAvatar => {
+    return {
+        id: overrides && overrides.hasOwnProperty('id') ? overrides.id! : '89f515e7-31e0-461d-a230-c4c7f4dafc5c',
+        avatar: overrides && overrides.hasOwnProperty('avatar') ? overrides.avatar! : anAvatar(),
+    };
+};
+"
+`;
+
 exports[`should use relationshipsToOmit argument to terminate circular relationships with terminateCircularRelationships enabled 1`] = `
 "
 export const anAbcType = (overrides?: Partial<AbcType>, relationshipsToOmit: Set<string> = new Set()): AbcType => {
@@ -1718,10 +1974,18 @@ export const aMutation = (overrides?: Partial<Mutation>, relationshipsToOmit: Se
     };
 };
 
+export const aPrefixedResponse = (overrides?: Partial<PrefixedResponse>, relationshipsToOmit: Set<string> = new Set()): PrefixedResponse => {
+    relationshipsToOmit.add('PrefixedResponse');
+    return {
+        ping: overrides && overrides.hasOwnProperty('ping') ? overrides.ping! : 'sunt',
+    };
+};
+
 export const aQuery = (overrides?: Partial<Query>, relationshipsToOmit: Set<string> = new Set()): Query => {
     relationshipsToOmit.add('Query');
     return {
         user: overrides && overrides.hasOwnProperty('user') ? overrides.user! : relationshipsToOmit.has('User') ? {} as User : aUser({}, relationshipsToOmit),
+        prefixed_query: overrides && overrides.hasOwnProperty('prefixed_query') ? overrides.prefixed_query! : relationshipsToOmit.has('Prefixed_Response') ? {} as Prefixed_Response : aPrefixedResponse({}, relationshipsToOmit),
     };
 };
 
diff --git a/tests/typescript-mock-data.spec.ts b/tests/typescript-mock-data.spec.ts
index f166245..f03e3a5 100644
--- a/tests/typescript-mock-data.spec.ts
+++ b/tests/typescript-mock-data.spec.ts
@@ -35,6 +35,11 @@ const testSchema = buildSchema(/* GraphQL */ `
 
     type Query {
         user: User!
+        prefixed_query: Prefixed_Response!
+    }
+
+    type Prefixed_Response {
+        ping: String!
     }
 
     type ABCType {
@@ -89,7 +94,7 @@ it('should generate mock data functions with external types file import', async
 
     expect(result).toBeDefined();
     expect(result).toContain(
-        "import { AbcType, Avatar, CamelCaseThing, Mutation, Query, UpdateUserInput, User, WithAvatar, AbcStatus, Status } from './types/graphql';",
+        "import { AbcType, Avatar, CamelCaseThing, Mutation, PrefixedResponse, Query, UpdateUserInput, User, WithAvatar, AbcStatus, Status } from './types/graphql';",
     );
     expect(result).toMatchSnapshot();
 });
@@ -305,7 +310,7 @@ it('should add enumsPrefix to imports', async () => {
 
     expect(result).toBeDefined();
     expect(result).toContain(
-        "import { AbcType, Avatar, CamelCaseThing, Mutation, Query, UpdateUserInput, User, WithAvatar, Api } from './types/graphql';",
+        "import { AbcType, Avatar, CamelCaseThing, Mutation, PrefixedResponse, Query, UpdateUserInput, User, WithAvatar, Api } from './types/graphql';",
     );
     expect(result).toMatchSnapshot();
 });
@@ -330,7 +335,7 @@ it('should not merge imports into one if typesPrefix does not contain dots', asy
 
     expect(result).toBeDefined();
     expect(result).toContain(
-        "import { ApiAbcType, ApiAvatar, ApiCamelCaseThing, ApiMutation, ApiQuery, ApiUpdateUserInput, ApiUser, ApiWithAvatar, AbcStatus, Status } from './types/graphql';",
+        "import { ApiAbcType, ApiAvatar, ApiCamelCaseThing, ApiMutation, ApiPrefixedResponse, ApiQuery, ApiUpdateUserInput, ApiUser, ApiWithAvatar, AbcStatus, Status } from './types/graphql';",
     );
     expect(result).toMatchSnapshot();
 });
@@ -343,7 +348,7 @@ it('should not merge imports into one if enumsPrefix does not contain dots', asy
 
     expect(result).toBeDefined();
     expect(result).toContain(
-        "import { AbcType, Avatar, CamelCaseThing, Mutation, Query, UpdateUserInput, User, WithAvatar, ApiAbcStatus, ApiStatus } from './types/graphql';",
+        "import { AbcType, Avatar, CamelCaseThing, Mutation, PrefixedResponse, Query, UpdateUserInput, User, WithAvatar, ApiAbcStatus, ApiStatus } from './types/graphql';",
     );
     expect(result).toMatchSnapshot();
 });
@@ -357,3 +362,19 @@ it('should use relationshipsToOmit argument to terminate circular relationships
     expect(result).not.toMatch(/: anAvatar\(\)/);
     expect(result).toMatchSnapshot();
 });
+
+it('should preserve underscores if transformUnderscore is false', async () => {
+    const result = await plugin(testSchema, [], {
+        transformUnderscore: false,
+        typesFile: './types/graphql.ts',
+    });
+
+    expect(result).toBeDefined();
+    expect(result).toContain(
+        "import { AbcType, Avatar, CamelCaseThing, Mutation, Prefixed_Response, Query, UpdateUserInput, User, WithAvatar, AbcStatus, Status } from './types/graphql';",
+    );
+    expect(result).toContain(
+        'export const aPrefixed_Response = (overrides?: Partial<Prefixed_Response>): Prefixed_Response => {',
+    );
+    expect(result).toMatchSnapshot();
+});