diff --git a/pyxform/constants.py b/pyxform/constants.py
index 6f42bb4f1..f27f5cf70 100644
--- a/pyxform/constants.py
+++ b/pyxform/constants.py
@@ -68,6 +68,7 @@
 # The following are the possible sheet names:
 SURVEY = "survey"
 SETTINGS = "settings"
+EXTERNAL_CHOICES = "external_choices"
 # These sheet names are for list sheets
 CHOICES_AND_COLUMNS = "choices and columns"
 CASCADING_CHOICES = "cascades"
@@ -84,6 +85,7 @@
     COLUMNS,
     CHOICES_AND_COLUMNS,
     SETTINGS,
+    EXTERNAL_CHOICES,
     OSM,
 ]
 SUPPORTED_FILE_EXTENSIONS = [".xls", ".xlsx", ".xlsm"]
diff --git a/pyxform/tests_v1/test_support_external_instances.py b/pyxform/tests_v1/test_support_external_instances.py
index 1c3714f8b..60810f260 100644
--- a/pyxform/tests_v1/test_support_external_instances.py
+++ b/pyxform/tests_v1/test_support_external_instances.py
@@ -165,3 +165,52 @@ def test_non_existent_itext_reference(self):
       </itemset>"""
             ],
         )
+
+    def test_external_choices_sheet_values_required(self):
+        md = """
+            | survey           |                               |          |           |                                     |
+            |                  | type                          | name     | label     | choice_filter                       |
+            |                  | text                          | S1       | s1        |                                     |
+            |                  | select_one_external counties  | county   | county    | S1=${S1}                            |
+            |                  | select_one_external cities    | city     | city      | S1=${S1} and county=${county}       |
+            | choices          |                               |          |           |
+            |                  | list name                     | name     | label     |
+            |                  | list                          | option a | a         |
+            | external_choices |              |                |
+            |                  | list_name    | name           |
+            |                  | counties     | Kajiado        |
+            |                  | counties     | Nakuru         |
+            |                  | cities       | Kisumu         |
+            |                  | cities       | Mombasa        |
+            """
+        expected = [
+            """<itemset nodeset="instance('cities')/root/item">
+            <value ref="name"/>
+            <label ref="label"/>
+            </itemset>"""
+        ]  # noqa
+        self.assertPyxformXform(
+            md=md, debug=True, model__contins=[expected], run_odk_validate=True
+        )
+
+    def test_list_name_not_in_external_choices_sheet_raises_error(self):
+        self.assertPyxformXform(
+            md="""
+                | survey           |                              |                |           |                                     |
+                |                  | type                         | name           | label     | choice_filter                       |
+                |                  | select_one list              | S1             | s1        |                                     |
+                |                  | select_one_external counties | county         | County    | S1=${S1}                            |
+                |                  | select_one_external cities   | city           | City      | S1=${S1} and county=${county}       |
+                | choices          |                              |                |           |
+                |                  | list name                    | name           | label     |
+                |                  | list                         | option a       | a         |
+                |                  | list                         | option b       | b         |
+                |                  | list                         | option c       | c         |
+                | external_choices |                              |                |
+                |                  | list_name                    | name           |
+                |                  | counties                     | Kajiado        |
+                |                  | counties                     | Nakuru         |
+                """,  # noqa
+            errored=True,
+            error__contains=["List name not in external choices sheet: cities"],
+        )
diff --git a/pyxform/xls2json.py b/pyxform/xls2json.py
index 9cb681025..bda1feb58 100644
--- a/pyxform/xls2json.py
+++ b/pyxform/xls2json.py
@@ -406,6 +406,19 @@ def workbook_to_json(
     # Here the default settings are overridden by those in the settings sheet
     json_dict.update(settings)
 
+    # ########## External Choices sheet ##########
+
+    external_choices_sheet = workbook_dict.get(constants.EXTERNAL_CHOICES, [])
+    for choice_item in external_choices_sheet:
+        replace_smart_quotes_in_dict(choice_item)
+
+    external_choices_sheet = dealias_and_group_headers(
+        external_choices_sheet, aliases.list_header, use_double_colons, default_language
+    )
+    external_choices = group_dictionaries_by_key(
+        external_choices_sheet, constants.LIST_NAME
+    )
+
     # ########## Choices sheet ##########
     # Columns and "choices and columns" sheets are deprecated,
     # but we combine them with the choices sheet for backwards-compatibility.
@@ -998,10 +1011,18 @@ def replace_prefix(d, prefix):
                         + " select one external is only meant for"
                         " filtered selects."
                     )
-                    select_type = aliases.select["select_one"]
                 list_name = parse_dict["list_name"]
                 list_file_name, file_extension = os.path.splitext(list_name)
-
+                if (
+                    select_type == "select one external"
+                    and list_name not in external_choices
+                ):
+                    raise PyXFormError(
+                        row_format_string % row_number
+                        + "List name not in external choices sheet: "
+                        + list_name
+                    )
+                    select_type = aliases.select["select_one"]
                 if (
                     list_name not in choices
                     and select_type != "select one external"