diff --git a/reference/mongo/mongocollection/ensureindex.xml b/reference/mongo/mongocollection/ensureindex.xml
index edd23f368e..dba8d549b6 100644
--- a/reference/mongo/mongocollection/ensureindex.xml
+++ b/reference/mongo/mongocollection/ensureindex.xml
@@ -60,9 +60,11 @@
          </para>
          <warning>
           <para>
-           A unique index cannot be created on a field if multiple existing documents do
-           not contain the field.  The field is effectively &null; for these documents 
-           and thus already non-unique.
+           A unique index cannot be created on a field if multiple existing
+           documents do not contain the field. The field is effectively &null;
+           for these documents and thus already non-unique. Sparse indexing may
+           be used to overcome this, since it will prevent documents without the
+           field from being indexed.
           </para>
          </warning>
         </listitem>
@@ -75,6 +77,32 @@
           all but one duplicate value.
          </para>
         </listitem>
+        <listitem>
+         <para>
+          <literal>"sparse"</literal>
+         </para>
+         <para>
+          Create a sparse index, which only includes documents containing the
+          field. This option is only compatible with single-field indexes.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+          <literal>"expireAfterSeconds"</literal>
+         </para>
+         <para>
+          The value of this option should specify the number of seconds after
+          which a document should be considered expired and automatically
+          removed from the collection. This option is only compatible with
+          single-field indexes where the field will contain
+          <classname>MongoDate</classname> values.
+         </para>
+         <para>
+          This feature is available in MongoDB 2.2+. See
+          <link xlink:href="&url.mongodb.docs.expire_data;">Expire Data from Collections by Setting TTL</link>
+          for more information.
+         </para>
+        </listitem>
         <listitem>
          <para>
           <literal>"background"</literal>