For example, Assume that I'm in form 1 then I want:
Steve's solution does not work. When calling this.Close(), current form is disposed together with form2. Therefore you need to hide it and set form2.Closed event to call this.Close().
private void OnButton1Click(object sender, EventArgs e)
{
this.Hide();
var form2 = new Form2();
form2.Closed += (s, args) => this.Close();
form2.Show();
}