diff --git a/src/Service.js b/src/Service.js
index bfe034fc..5f31e47a 100644
--- a/src/Service.js
+++ b/src/Service.js
@@ -457,6 +457,20 @@ Service_.prototype.getAccessToken = function() {
   return token.access_token;
 };
 
+/**
+ * Gets an id token for this service. This token can be used in HTTP
+ * requests to the service's endpoint. This method will throw an error if the
+ * user's access was not granted or has expired.
+ * @return {string} An id token.
+ */
+Service_.prototype.getIdToken = function() {
+  if (!this.hasAccess()) {
+    throw new Error('Access not granted or expired.');
+  }
+  var token = this.getToken();
+  return token.id_token;
+};
+
 /**
  * Resets the service, removing access and requiring the service to be
  * re-authorized.