diff --git a/reference/mongo/mongocollection/ensureindex.xml b/reference/mongo/mongocollection/ensureindex.xml
index 7ac84416f5..41f2b45ed7 100644
--- a/reference/mongo/mongocollection/ensureindex.xml
+++ b/reference/mongo/mongocollection/ensureindex.xml
@@ -63,6 +63,17 @@
           all but one duplicate value.
          </para>
         </listitem>
+        <listitem>
+         <para>
+          <literal>"background"</literal>
+         </para>
+         <para>
+          If you are using MongoDB version 1.3.2+, you can create indexes in the
+          background while other operations are taking place.  By default, index
+          creation happens synchronously.  If you specify &true; with this 
+          option, index creation will be asynchronous.
+         </para>
+        </listitem>
        </itemizedlist>
       </para>
      </listitem>