diff --git a/README.md b/README.md
index 3107b255..5486b220 100644
--- a/README.md
+++ b/README.md
@@ -84,6 +84,7 @@ or to be supported, or well, for starters, to be a good idea.
   - [Service for `select`: Select random option](#service-for-select-select-random-option)
 - [Repairs](#repairs)
   - [Automations: Find use of non-existing areas, devices and entities](#automations-find-use-of-non-existing-areas-devices-and-entities)
+  - [Groups: Detect unknown group members](#groups-detect-unknown-group-members)
   - [Obsolete integration YAML configuration](#obsolete-integration-yaml-configuration)
   - [Scripts: Find use of non-existing areas, devices and entities](#scripts-find-use-of-non-existing-areas-devices-and-entities)
 - [Frequently Asked Questions](#frequently-asked-questions)
@@ -416,6 +417,12 @@ Currently Spook will detect the following issues:
 _Intention to contribute back to Home Assistant Core once sure no false
 postives remain, and it has been extended to catch more situations._
 
+## Groups: Detect unknown group members
+
+> Finds groups that contain references to unknown members (entities). _#aliens_
+
+_Intention to contribute back to Home Assistant Core._
+
 ## Obsolete integration YAML configuration
 
 > Finds YAML configuration for an integrations that no longer support it.
diff --git a/custom_components/spook/repairs/group_unknown_members.py b/custom_components/spook/repairs/group_unknown_members.py
new file mode 100644
index 00000000..2d0cdf00
--- /dev/null
+++ b/custom_components/spook/repairs/group_unknown_members.py
@@ -0,0 +1,108 @@
+"""Spook - Not your homie."""
+from __future__ import annotations
+
+from homeassistant.components import group
+from homeassistant.const import (
+    ENTITY_MATCH_ALL,
+    ENTITY_MATCH_NONE,
+    EVENT_COMPONENT_LOADED,
+)
+from homeassistant.helpers import entity_registry as er
+from homeassistant.helpers.entity_platform import DATA_ENTITY_PLATFORM, EntityPlatform
+
+from ..const import LOGGER
+from . import AbstractSpookRepair
+
+
+class SpookRepair(AbstractSpookRepair):
+    """Spook repair tries to find unknown member entities in groups."""
+
+    domain = group.DOMAIN
+    repair = "group_unknown_members"
+    events = {
+        EVENT_COMPONENT_LOADED,
+        er.EVENT_ENTITY_REGISTRY_UPDATED,
+        "event_group_reloaded",
+        "event_input_boolean_reloaded",
+        "event_input_button_reloaded",
+        "event_input_number_reloaded",
+        "event_input_select_reloaded",
+        "event_input_text_reloaded",
+        "event_integration_reloaded",
+        "event_min_max_reloaded",
+        "event_mqtt_reloaded",
+        "event_scene_reloaded",
+        "event_schedule_reloaded",
+        "event_template_reloaded",
+        "event_threshold_reloaded",
+        "event_tod_reloaded",
+        "event_utility_meter_reloaded",
+    }
+
+    _entity_platforms: list[EntityPlatform]
+
+    async def async_activate(self) -> None:
+        """Handle the activating a repair."""
+        self._entity_platforms = self.hass.data[DATA_ENTITY_PLATFORM][self.domain]
+        await super().async_activate()
+
+    async def async_inspect(self) -> None:
+        """Trigger a inspection."""
+        LOGGER.debug("Spook is inspecting: %s", self.repair)
+
+        # Two sources for entities. The entities in the entity registry,
+        # and the entities currently in the state machine. They will have lots
+        # of overlap, but not all entities are in the entity registry and
+        # not all have to be in the state machine right now.
+        # Furthermore, add `all` and `none` to the list of known entities,
+        # as they are valid targets.
+        entity_ids = (
+            {entity.entity_id for entity in self.entity_registry.entities.values()}
+            .union(self.hass.states.async_entity_ids())
+            .union({ENTITY_MATCH_ALL, ENTITY_MATCH_NONE})
+        )
+
+        for platform in self._entity_platforms:
+            # We don't want to check the old style group platform
+            for entity in platform.entities.values():
+                members = []
+                if platform.domain == group.DOMAIN:
+                    members = entity.tracking
+                elif hasattr(entity, "_entity_ids"):
+                    # pylint: disable-next=protected-access
+                    members = entity._entity_ids  # noqa: SLF001
+                elif hasattr(entity, "_entities"):
+                    # pylint: disable-next=protected-access
+                    members = entity._entities  # noqa: SLF001
+
+                # Filter out scenes, groups & device_tracker entities.
+                # Those can be created on the fly with services, which we
+                # currently cannot detect yet. Let's prevent some false positives.
+                if unknown_entities := {
+                    entity_id
+                    for entity_id in members
+                    if (
+                        not entity_id.startswith(
+                            ("device_tracker.", "group.", "scene."),
+                        )
+                        and entity_id not in entity_ids
+                    )
+                }:
+                    self.async_create_issue(
+                        issue_id=entity.entity_id,
+                        translation_placeholders={
+                            "entities": "\n".join(
+                                f"- `{entity_id}`" for entity_id in unknown_entities
+                            ),
+                            "group": entity.name,
+                            "entity_id": entity.entity_id,
+                        },
+                    )
+                    LOGGER.debug(
+                        "Spook found unknown member entities in %s "
+                        "and created an issue for it; Entities: %s",
+                        entity.entity_id,
+                        ", ".join(unknown_entities),
+                    )
+                else:
+                    self.async_delete_issue(entity.entity_id)
diff --git a/custom_components/spook/translations/en.json b/custom_components/spook/translations/en.json
index b2174fc8..38ac1d82 100644
--- a/custom_components/spook/translations/en.json
+++ b/custom_components/spook/translations/en.json
@@ -33,6 +33,10 @@
       "title": "Unknown entities used in: {automation}",
       "description": "Spook has found a ghost in your automations 👻\n\nWhile floating around, Spook crossed path with the following automation:\n\n[{automation}]({edit}) (`{entity_id}`)\n\nThis automation references the following entities, which are unknown to Home Assistant:\n\n{entities}\n\n\n\nTo fix this error, [edit the automation]({edit}) and remove the use of these non-existing entities.\n\nSpook 👻 Not your homie."
     },
+    "group_unknown_members": {
+      "title": "Unknown group members in: {group}",
+      "description": "Spook has found a ghost in your groups 👻\n\nWhile floating around, Spook crossed path with the following group:\n\n{group} (`{entity_id}`)\n\nThis group has members, which are unknown to Home Assistant:\n\n{entities}\n\n\n\nTo fix this error, edit the group, remove the use of these non-existing entities and restart Home Assistant.\n\nSpook 👻 Not your homie."
+    },
     "obsolete_integration_yaml_config": {
       "title": "Obsolete YAML for: {domain}",
       "description": "Spook has found a ghost in your YAML configuration 👻\n\nWhile floating around, Spook came aroud YAML configuration for the `{domain}` integration, which is obsolete (as it is no longer configured via YAML) and thus should be removed/cleaned up. This issue will automatically disappear once your configuration has been adjusted and Home Assistant has been restarted.\n\nSpook 👻 Not your homie."