hello I am developing an kind of outlook calendar application where I need to make the appointment resizable from mouse. My first try with a thumb did not work properly so I tried another way. What I did is that: 1) on the botton of the appointmennt panel I added a rectangle to figure out the resize zone (the thumb). The appointment panel is put on a grid panel. 2) I intercept down event on the rectangle and send event to this code: private Point startPoint; private void OnResizeElementMouseDown(object sender, MouseButtonEventArgs e) { e.Handled = true; this.MouseMove += new MouseEventHandler(ResizeEndElement_MouseMove); this.MouseLeftButtonUp += new MouseButtonEventHandler(OnResizeElementMouseUp); // some code to perform new height computation Mouse.Capture(this); } where this is the appointment panel that own the thumb. Decreasing height works well. But increasing is more difficult. If I move the mouse very very slowly it's OK, if I speed it up a little bit it tends to leave out the appointment panel and then all MouseMove event are lost. I thought Mouse.Capture() was propose to solve this kind of problem, but in fact not. Does anybody know what is wrong in my code?