This is how I run only once a form in an MDI enviroment

private frmOrders objOrders=null;


try
{
//frmOrders objOrders=null;
foreach(Form f in this.MdiChildren)
{
if(f is frmOrders) //found it
{
objOrders=(frmOrders) f;
break;
}
}
if(objOrders != null && objOrders.IsDisposed==false)
{
objOrders.Show();
objOrders.Focus();
}
else
{
objOrders=new frmOrders();
objOrders.Show();
objOrders.Focus();
}
}
catch(Exception eo)
{
MessageBox.Show("Error \n" + eo.Message,
"Error",
MessageBoxButtons.OK,
MessageBoxIcon.Error);
}