I'm on a brief professional training program with the Air Force, and was recently assigned to the COM squadron on base. There is no way at least %50 of those guys don't have at least mild AS. Their gait, how they talked, what they thought was funny, they seemed to have no clue whatsoever that the extremely complicated com parts they were describing were a) impossible to understand, and b) extremely boring...all dead giveaways.
To answer your question though, at least for the Air Force, I have gone over the AFI (our regulations) and there is nothing that prevents people with autistic-spectrum disorders from either enlisting or commissioning. There ARE, however, regulations against personality disorders, mood disorders, and anxiety disorders, explicitly laid out. If you have taken any medication in the past year, you are prohibited. I was advised by one of my commanders (informally) that if you go off meds for a year, you are good to go (no need to admit on medical record unless you are looking to start out being excluded from enlisting). However, the military generally does not enforce this, although certain career fields would probably weed those people out. The Armed Forces Journal just did a piece on how many people with mood, anxiety, etc disorders were enlisting and the recruiter tells them not to mention it again if the recruit tells them they have X disorder, etc. 99% of the time they will not even bother looking into it. (Although following some sort of psychiatric meltdown, an evaluation and history will definitely be done). I'm going in as an officer anyway. This is the only thing I can imagine doing, and I've been finding other people who should 100% not be in (asthma, current and ongoing weed use, etc). If you want to do it, you cannot do enough research. Here's a good link about enlisting (although it doesn't cover AS specifically, just any question you can think of): http://forums.somethingawful.com/showth ... genumber=1