private void btnReservations_Click(object sender, EventArgs e) { foreach (Form f in Application.OpenForms) { if (f.GetType() == typeof(Reservations)) { f.WindowState = System.Windows.Forms.FormWindowState.Maximized; return; } } Reservations m = new Reservations(); m.MdiParent = this; m.WindowState = FormWindowState.Maximized; m.Show(); }