Autism and Gender: Are there differences?
From Autism Vox: Discussion of whether autism is different in females, and whether they are underdiagnosed.

http://specialchildren.about.com/gi/dynamic/offsite.htm?zi=1/XJ/Ya&sdn=specialchildren&zu=http%3A%2F%2Fwww.autismvox.com%2Fautism-and-gender-are-there-differences%2F

When I went to an autism training session last year, the speaker thought that girls were definitely under diagnosed. He felt that a girl with Asperger's syndrome might be able to blend in better than a boy would, because he thought there were greater variances in what is percieved as "normal" for girls than boys. I don't know, though.