diff --git a/Implab/PromiseExtensions.cs b/Implab/PromiseExtensions.cs
--- a/Implab/PromiseExtensions.cs
+++ b/Implab/PromiseExtensions.cs
@@ -72,6 +72,23 @@ namespace Implab {
                 }
             };
         }
+
+        static void CancelCallback(object cookie) {
+            ((ICancellable)cookie).Cancel();
+        }
+
+        /// <summary>
+        /// Cancells promise after the specified timeout is elapsed.
+        /// </summary>
+        /// <param name="that">The promise to cancel on timeout.</param>
+        /// <param name="milliseconds">The timeout in milliseconds.</param>
+        /// <typeparam name="TPromise">The 1st type parameter.</typeparam>
+        public static TPromise Timeout<TPromise>(this TPromise that, int milliseconds) where TPromise : IPromise {
+            Safe.ArgumentNotNull(that, "that");
+            var timer = new Timer(CancelCallback, that, milliseconds, -1);
+            that.On(timer.Dispose, PromiseEventType.All);
+            return that;
+        }
             
         #if NET_4_5