It sounds like you have built an MDI application - in this case, all the children are contained within the border of the parent application, and cannot be any larger than the client area of the parent. You can make a child fill teh parent client area very easily: just set the WindowState property to FormWindowState.Maximized but you cannot make it fill the screen, or appear outside the bound of the parent. Step to Create and Implement MDI Child Form. Create a MDI parent form with a MenuStrip which containing the values New and Windows and Close in the sub menu of New. Now go to Properties Window, select the all menu items and set the the MdiList property to true. Create MDI child forms. Create a new Windows Forms application project in Visual Studio. In the Properties window for the form, set its IsMdiContainer property to true and its WindowsState property to Maximized. This designates the form as an MDI container for child windows. From the Toolbox, drag a MenuStrip control to the form.