diff --git a/src/applications/people/controller/PhabricatorPeopleLdapController.php b/src/applications/people/controller/PhabricatorPeopleLdapController.php
--- a/src/applications/people/controller/PhabricatorPeopleLdapController.php
+++ b/src/applications/people/controller/PhabricatorPeopleLdapController.php
@@ -149,6 +149,9 @@
 
     $results = $ldap_adapter->searchLDAP('%Q', $search);
 
+    $existing_users = id(new PhabricatorPeopleQuery())->execute();
+    $existing_users = (mpull($existing_users, 'getUserName'));
+
     foreach ($results as $key => $record) {
       $account_id = $ldap_adapter->readLDAPRecordAccountID($record);
       if (!$account_id) {
@@ -161,8 +164,12 @@
         $ldap_adapter->readLDAPRecordEmail($record),
         $ldap_adapter->readLDAPRecordRealName($record),
       );
-      $results[$key] = $info;
-      $results[$key][] = $this->renderUserInputs($info);
+
+      if (!in_array(strtolower(idx($info, 0)), $existing_users) &&
+        !in_array(strtoupper(idx($info, 0)), $existing_users)) {
+        $results[$key] = $info;
+        $results[$key][] = $this->renderUserInputs($info);
+      }
     }
 
     $form = id(new AphrontFormView())