Why the form in closed when a click a button?

I've 2 forms, in the first form I've a menu, in the click event of one of the items of the menu I've the next code: (new Form2()).ShowDialog(this); This code open the second form. In the second form I've a button, but this button it doesn't have code and when I Click the button the form is closed. Sombody can tell me Why. Thanks.