Well, I'm no expert but I wouldn't give up just yet.
It it genetic as MackTheKnife said, but it doesn't mean death sentence for your hair.
I spend some time reading an article about treatments in wikipedia, and there is hope. Maybe you will have to wait to currently developed treatments, but you can check out those have a varying rate of success.
http://en.wikipedia.org/wiki/Baldness_treatments
In contrast to the above, you can always go mega-bald! My friend did it, and it looks pretty good, and much better than only some hair.