Hi, I have an app which consists of a Main Window and 10 or so client windows. However, I need the app to work like an SDI in that only one window is visible at a time and that window should be maximized. If I set all my child windows to have WindowState.Maximized this kind of works, but after switching windows 4 or 5 times, I end up with all the windows showing but not maximized. I have tried various things including overriding OnActivated, OnResizing, OnSizeChanged and changing the windowstate and window size but none seem to work. Where should I be looking? Is this controlled by the child forms or the MDI Parent? Thanks for any help Cheers James