Technically, you should because full-screen operation is exactly the same as windowed except that your window has only client area and takes up the whole screen. As such, there are scenarios under which the contents of your client area may be overwritten, though they''re rare. In both windowed and full-screen modes, WM_PAINT handling isn''t truly necessary, assuming that you repaint your client area at a regular interval. But your app will look better if you handle it. So, I recommend that you handle it—it''s sufficiently trivial to do.