check for subpages?

I’ve added a subpage listing to my template and I want to add a header before the listing but only when there are subpages. Right now, my header appears all the time like this:

<h2>See Also</h2>
wp_list_pages('title_li=&depth=3&child_of='.$post->ID );

There must be a piece of code to test if there are subpages or count subpages, any ideas?