diff --git a/changelog.d/4895.feature b/changelog.d/4895.feature
new file mode 100644
index 0000000000..5dd7c68194
--- /dev/null
+++ b/changelog.d/4895.feature
@@ -0,0 +1 @@
+Add option to disable searching the user directory.
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index d72b90a37b..f6f6aec7cf 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -962,6 +962,10 @@ password_config:
 
 # User Directory configuration
 #
+# 'enabled' defines whether users can search the user directory. If
+# false then empty responses are returned to all queries. Defaults to
+# true.
+#
 # 'search_all_users' defines whether to search all users visible to your HS
 # when searching the user directory, rather than limiting to users visible
 # in public rooms.  Defaults to false.  If you set it True, you'll have to run
@@ -969,6 +973,7 @@ password_config:
 # on your database to tell it to rebuild the user_directory search indexes.
 #
 #user_directory:
+#  enabled: true
 #  search_all_users: false
 
 
diff --git a/synapse/config/user_directory.py b/synapse/config/user_directory.py
index fab3a7d1c8..142754a7dc 100644
--- a/synapse/config/user_directory.py
+++ b/synapse/config/user_directory.py
@@ -22,9 +22,13 @@ class UserDirectoryConfig(Config):
     """
 
     def read_config(self, config):
+        self.user_directory_search_enabled = True
         self.user_directory_search_all_users = False
         user_directory_config = config.get("user_directory", None)
         if user_directory_config:
+            self.user_directory_search_enabled = (
+                user_directory_config.get("enabled", True)
+            )
             self.user_directory_search_all_users = (
                 user_directory_config.get("search_all_users", False)
             )
@@ -33,6 +37,10 @@ class UserDirectoryConfig(Config):
         return """
         # User Directory configuration
         #
+        # 'enabled' defines whether users can search the user directory. If
+        # false then empty responses are returned to all queries. Defaults to
+        # true.
+        #
         # 'search_all_users' defines whether to search all users visible to your HS
         # when searching the user directory, rather than limiting to users visible
         # in public rooms.  Defaults to false.  If you set it True, you'll have to run
@@ -40,5 +48,6 @@ class UserDirectoryConfig(Config):
         # on your database to tell it to rebuild the user_directory search indexes.
         #
         #user_directory:
+        #  enabled: true
         #  search_all_users: false
         """
diff --git a/synapse/rest/client/v2_alpha/user_directory.py b/synapse/rest/client/v2_alpha/user_directory.py
index cac0624ba7..36b02de37f 100644
--- a/synapse/rest/client/v2_alpha/user_directory.py
+++ b/synapse/rest/client/v2_alpha/user_directory.py
@@ -59,6 +59,12 @@ class UserDirectorySearchRestServlet(RestServlet):
         requester = yield self.auth.get_user_by_req(request, allow_guest=False)
         user_id = requester.user.to_string()
 
+        if not self.hs.config.user_directory_search_enabled:
+            defer.returnValue((200, {
+                "limited": False,
+                "results": [],
+            }))
+
         body = parse_json_object_from_request(request)
 
         limit = body.get("limit", 10)
diff --git a/tests/handlers/test_user_directory.py b/tests/handlers/test_user_directory.py
index aefe11ac28..f1d0aa42b6 100644
--- a/tests/handlers/test_user_directory.py
+++ b/tests/handlers/test_user_directory.py
@@ -16,6 +16,7 @@ from mock import Mock
 
 from synapse.api.constants import UserTypes
 from synapse.rest.client.v1 import admin, login, room
+from synapse.rest.client.v2_alpha import user_directory
 from synapse.storage.roommember import ProfileInfo
 
 from tests import unittest
@@ -317,3 +318,54 @@ class UserDirectoryTestCase(unittest.HomeserverTestCase):
         u4 = self.register_user("user4", "pass")
         s = self.get_success(self.handler.search_users(u1, u4, 10))
         self.assertEqual(len(s["results"]), 1)
+
+
+class TestUserDirSearchDisabled(unittest.HomeserverTestCase):
+    user_id = "@test:test"
+
+    servlets = [
+        user_directory.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+        admin.register_servlets,
+    ]
+
+    def make_homeserver(self, reactor, clock):
+        config = self.default_config()
+        config.update_user_directory = True
+        hs = self.setup_test_homeserver(config=config)
+
+        self.config = hs.config
+
+        return hs
+
+    def test_disabling_room_list(self):
+        self.config.user_directory_search_enabled = True
+
+        # First we create a room with another user so that user dir is non-empty
+        # for our user
+        self.helper.create_room_as(self.user_id)
+        u2 = self.register_user("user2", "pass")
+        room = self.helper.create_room_as(self.user_id)
+        self.helper.join(room, user=u2)
+
+        # Assert user directory is not empty
+        request, channel = self.make_request(
+            "POST",
+            b"user_directory/search",
+            b'{"search_term":"user2"}',
+        )
+        self.render(request)
+        self.assertEquals(200, channel.code, channel.result)
+        self.assertTrue(len(channel.json_body["results"]) > 0)
+
+        # Disable user directory and check search returns nothing
+        self.config.user_directory_search_enabled = False
+        request, channel = self.make_request(
+            "POST",
+            b"user_directory/search",
+            b'{"search_term":"user2"}',
+        )
+        self.render(request)
+        self.assertEquals(200, channel.code, channel.result)
+        self.assertTrue(len(channel.json_body["results"]) == 0)