diff --git src/bp-notifications/bp-notifications-functions.php src/bp-notifications/bp-notifications-functions.php
index a0a2169..c3f1a2a 100644
--- src/bp-notifications/bp-notifications-functions.php
+++ src/bp-notifications/bp-notifications-functions.php
@@ -421,6 +421,26 @@ function bp_notifications_delete_notifications_from_user( $user_id, $component_n
 	) );
 }
 
+/**
+ * Delete a user's notifications when the user is deleted.
+ *
+ * @since 2.5.0
+ *
+ * @param int $user_id  ID of the user who is about to be deleted.
+ * @return int|bool The number of rows updated or false on error.
+ */
+function bp_notifications_delete_notifications_on_user_delete( $user_id ) {
+	return BP_Notifications_Notification::delete( array(
+		'user_id'           => $user_id,
+		'item_id'           => false,
+		'secondary_item_id' => false,
+		'component_action'  => false,
+		'component_name'    => false
+	) );
+}
+add_action( 'wpmu_delete_user', 'bp_notifications_delete_notifications_on_user_delete' );
+add_action( 'delete_user', 'bp_notifications_delete_notifications_on_user_delete' );
+
 /** Mark **********************************************************************/
 
 /**