If your helmet hit the ground - replace it! As Emily said, our helmets are designed for a single crash.

Warning: don't go to this (linked) page if blood bothers you. It contains pictures of the helmet I was wearing when I crashed (wow, 2 years ago now). The first photo is a view from the side, and it's very difficult to see the remnants of the crash (other than the blood spots, that is). The second 2 pictures show the deep cracks that were the result of the crash. This previously uncrashed helmet saved my life... http://www.crazyguyonabike.com/journ...?page_id=12901

It's a bit more obvious after a crash like mine that the helmet needs to be replaced - but really, any time a helmet hits the ground it's time for a new one.

--- Denise