child form appears again after checking dialog result if ok

James,

Your code works, however it took me a couple of minutes how to work it out.

Thanks!

Try this out. The following code will prevent you to open duplicate form.
 
        foreach (Form frmchild in this.MdiChildren)
            {

                if (frmcompany is chldfrm)
                {

                    frmchild.Show();
                    frmchild.Focus();
                   
                    return;

                }

            }

            chldfrm frmchild1 = new chldfrm();
          
            this.AddOwnedForm(frmchild1);

            frmchild1.MdiParent = this;

            frmchild1.Show();