diff --git a/changelog.d/4445.feature b/changelog.d/4445.feature
new file mode 100644
index 000000000..a6f9b7bba
--- /dev/null
+++ b/changelog.d/4445.feature
@@ -0,0 +1 @@
+Add a metric for tracking event stream position of the user directory.
\ No newline at end of file
diff --git a/synapse/handlers/user_directory.py b/synapse/handlers/user_directory.py
index 3c4099933..120815b09 100644
--- a/synapse/handlers/user_directory.py
+++ b/synapse/handlers/user_directory.py
@@ -19,6 +19,7 @@ from six import iteritems
 
 from twisted.internet import defer
 
+import synapse.metrics
 from synapse.api.constants import EventTypes, JoinRules, Membership
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage.roommember import ProfileInfo
@@ -163,6 +164,11 @@ class UserDirectoryHandler(object):
                 yield self._handle_deltas(deltas)
 
                 self.pos = deltas[-1]["stream_id"]
+
+                # Expose current event processing position to prometheus
+                synapse.metrics.event_processing_positions.labels(
+                    "user_dir").set(self.pos)
+
                 yield self.store.update_user_directory_stream_pos(self.pos)
 
     @defer.inlineCallbacks