Thread.Sleep() & Application.DoEvents()

Practically, I can't think of any reason to prefer one over the other. I would choose neither. It is generally better practice to use a separate thread (say using a BackgroundWorker) for long-running background tasks instead of calling Application.DoEvents.

As for your actual question, there is a difference if the thread that it's running on is the message loop thread. If Sleep is called first, then there will be a 100 millisecond (0.1 second) delay in processing messages (fairly short, but noticeable if you are dragging the form at the time). If Sleep is called after, there will still be a delay, but if there was a long running process already before -- long enough to build up messages -- it will wait an additional 100ms before processing. Try changing the 100 to a 5000 and see if you can tell any difference.

But if the thread where this code runs is not the message loop thread, then the message loop thread will still process any messages while this thread sleeps, so Application.DoEvents is unnecessary, and they will act equivalent.

Edit: Hmm, did you edit your question Or did I just not see your question for the right way to do this I would do this by launching another thread in a BackgroundWorker and do the waiting in that thread. Try searching for BackgroundWorker for numerous examples.