diff --git a/functions/src/clean-orphan-media.ts b/functions/src/clean-orphan-media.ts
new file mode 100644
index 000000000..d16e43fcc
--- /dev/null
+++ b/functions/src/clean-orphan-media.ts
@@ -0,0 +1,54 @@
+/**
+ * Copyright 2026 The Ground Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the 'License');
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an 'AS IS' BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { getFirestore } from 'firebase-admin/firestore';
+
+import { getStorageBucket } from './common/context';
+import { surveys } from './common/datastore';
+
+const USER_MEDIA_SURVEYS_PREFIX = 'user-media/surveys/';
+
+/**
+ * Deletes files under `user-media/surveys/{surveyId}/...` whose `surveyId`
+ * no longer corresponds to a live document in the `surveys` collection.
+ *
+ * Files are listed before surveys so that a survey created mid-run cannot
+ * have its just-uploaded media misclassified as orphaned.
+ */
+export async function cleanOrphanMediaHandler() {
+  const bucket = getStorageBucket();
+  const [files] = await bucket.getFiles({ prefix: USER_MEDIA_SURVEYS_PREFIX });
+
+  const surveysSnapshot = await getFirestore().collection(surveys()).get();
+  const liveSurveyIds = new Set(surveysSnapshot.docs.map(d => d.id));
+
+  const orphans = files.filter(f => {
+    const surveyId = surveyIdFromPath(f.name);
+    return surveyId !== null && !liveSurveyIds.has(surveyId);
+  });
+
+  await Promise.all(orphans.map(f => f.delete()));
+  console.log(
+    `Deleted ${orphans.length} orphan media file(s) under ${USER_MEDIA_SURVEYS_PREFIX}.`
+  );
+}
+
+function surveyIdFromPath(path: string): string | null {
+  if (!path.startsWith(USER_MEDIA_SURVEYS_PREFIX)) return null;
+  const rest = path.substring(USER_MEDIA_SURVEYS_PREFIX.length);
+  const slashIdx = rest.indexOf('/');
+  return slashIdx < 0 ? null : rest.substring(0, slashIdx);
+}
diff --git a/functions/src/index.ts b/functions/src/index.ts
index 0e7595bfd..899d1e691 100644
--- a/functions/src/index.ts
+++ b/functions/src/index.ts
@@ -27,6 +27,7 @@ import { importGeoJsonCallback } from './import-geojson';
 import { exportCsvHandler } from './export-csv';
 import { exportGeojsonHandler } from './export-geojson';
 import { cleanTempHandler } from './clean-temp';
+import { cleanOrphanMediaHandler } from './clean-orphan-media';
 import { onCall } from 'firebase-functions/v2/https';
 import { onCreateLoiHandler } from './on-create-loi';
 import { onCreatePasslistEntryHandler } from './on-create-passlist-entry';
@@ -110,3 +111,8 @@ export const onWriteSurvey = onDocumentWritten(
 export const sessionLogin = onHttpsRequest(sessionLoginHandler);
 
 export const cleanTemp = onSchedule('every 1 hours', cleanTempHandler);
+
+export const cleanOrphanMedia = onSchedule(
+  'every 24 hours',
+  cleanOrphanMediaHandler
+);