to open MDI form from Form1 and hide Form1

Question

Hi all!
please do help me. I have an MDI form and another form say Form1.I want to hide the Form1 on certain condition and want to open MDI form from Form1.If that particular condition is false I want to stay in Form1 itself.
When i gave code below both forms are visible. please help!
MDIParent1 md;
md = new MDIParent1();
md.Show();
this.Hide();// to hide Form1