diff --git a/api/segment_membership/tasks.py b/api/segment_membership/tasks.py
index 13c056127948..704ef7782ab6 100644
--- a/api/segment_membership/tasks.py
+++ b/api/segment_membership/tasks.py
@@ -161,6 +161,21 @@ def refresh_project_segment_counts(project_id: int) -> None:
         now = timezone.now()
         for m in membership_counts:
             m.last_synced_at = now
+
+        new_pairs = {(m.segment_id, m.environment_id) for m in membership_counts}
+        stale_ids = [
+            pk
+            for pk, segment_id, environment_id in (
+                SegmentMembershipCount.objects.filter(
+                    segment__project=project
+                ).values_list("id", "segment_id", "environment_id")
+            )
+            if (segment_id, environment_id) not in new_pairs
+        ]
+        stale_deleted, _ = SegmentMembershipCount.objects.filter(
+            id__in=stale_ids,
+        ).delete()
+
         SegmentMembershipCount.objects.bulk_create(
             membership_counts,
             update_conflicts=True,
@@ -171,4 +186,5 @@ def refresh_project_segment_counts(project_id: int) -> None:
             "refresh.project.completed",
             project__id=project_id,
             membership_counts__count=len(membership_counts),
+            stale_counts__count=stale_deleted,
         )
diff --git a/api/tests/unit/segment_membership/test_unit_segment_membership_tasks.py b/api/tests/unit/segment_membership/test_unit_segment_membership_tasks.py
index 9a57ae884f2a..3eff7ba86c38 100644
--- a/api/tests/unit/segment_membership/test_unit_segment_membership_tasks.py
+++ b/api/tests/unit/segment_membership/test_unit_segment_membership_tasks.py
@@ -1,5 +1,6 @@
 from unittest.mock import MagicMock
 
+from django.utils import timezone
 from pytest_django.fixtures import SettingsWrapper
 from pytest_mock import MockerFixture
 from pytest_structlog import StructuredLogCapture
@@ -295,3 +296,63 @@ def test_refresh_project_segment_counts__counts_returned__upserts_per_env_rows(
             f":project_{project.id}"
         )
     )
+
+
+def test_refresh_project_segment_counts__previously_matching_pair_drops_to_zero__row_deleted(
+    mocker: MockerFixture,
+    settings: SettingsWrapper,
+    project: Project,
+    environment: Environment,
+    segment: Segment,
+    enable_features: EnableFeaturesFixture,
+) -> None:
+    # Given a prior refresh that landed a non-zero count for (segment, env)
+    enable_features("segment_membership_inspection")
+    settings.CLICKHOUSE_ENABLED = True
+    SegmentMembershipCount.objects.create(
+        segment=segment,
+        environment=environment,
+        count=15,
+        last_synced_at=timezone.now(),
+    )
+    cursor = MagicMock()
+    open_cursor = mocker.patch.object(tasks, "open_clickhouse_cursor")
+    open_cursor.return_value.__enter__.return_value = cursor
+    # ... and a new compute that returns no matches for the same pair (the
+    # rule was edited, the identity set drifted, etc.).
+    mocker.patch.object(tasks, "compute_segment_counts_for_project", return_value=[])
+
+    # When
+    refresh_project_segment_counts(project.id)
+
+    # Then the stale row is gone -- pairs that no longer match drop out of
+    # the table entirely rather than lingering at the previous count.
+    assert not SegmentMembershipCount.objects.filter(
+        segment=segment, environment=environment
+    ).exists()
+
+
+def test_refresh_project_segment_counts__never_matched_pair__no_row_written(
+    mocker: MockerFixture,
+    settings: SettingsWrapper,
+    project: Project,
+    environment: Environment,
+    segment: Segment,
+    enable_features: EnableFeaturesFixture,
+) -> None:
+    # Given a project with no prior membership rows
+    enable_features("segment_membership_inspection")
+    settings.CLICKHOUSE_ENABLED = True
+    cursor = MagicMock()
+    open_cursor = mocker.patch.object(tasks, "open_clickhouse_cursor")
+    open_cursor.return_value.__enter__.return_value = cursor
+    mocker.patch.object(tasks, "compute_segment_counts_for_project", return_value=[])
+
+    # When
+    refresh_project_segment_counts(project.id)
+
+    # Then no row is written: refresh upserts matches, drops misses, and
+    # leaves never-matched pairs untouched.
+    assert not SegmentMembershipCount.objects.filter(
+        segment=segment, environment=environment
+    ).exists()
diff --git a/docs/docs/deployment-self-hosting/observability/_events-catalogue.md b/docs/docs/deployment-self-hosting/observability/_events-catalogue.md
index 2ddb52d2f39b..eb0ad2df9312 100644
--- a/docs/docs/deployment-self-hosting/observability/_events-catalogue.md
+++ b/docs/docs/deployment-self-hosting/observability/_events-catalogue.md
@@ -368,11 +368,12 @@ Attributes:
 ### `segment_membership.refresh.project.completed`
 
 Logged at `info` from:
- - `api/segment_membership/tasks.py:170`
+ - `api/segment_membership/tasks.py:185`
 
 Attributes:
  - `membership_counts.count`
  - `project.id`
+ - `stale_counts.count`
 
 ### `segment_membership.refresh.project.failed`