It's not an easy question to answer:
http://www.saafe.info/main/index.php?topic=86.msg565#msg565 for some of the reasons.
Although they're ten years old and they don't give figures as to risk, the best summary I know of is still contained in two articles in the journal
Sexually Transmitted Infections, one looking at viral STIs and one at the non-virals.
Having said that... you can catch things like gonorrhoea, syphilis, chlamydia etc, but these are all curable and discreet checks of his penis will spot most cases before it goes in your mouth (a couple of hundred years ago a book for wives advised squeezing the flaccid penis - if pus comes out or the owner goes 'ouch', send them to the doctor.)
There's a vaccine for HepB which you should strongly consider having and if you're unlucky enough to get HIV this way, you're probably already dead. You can catch HSV 1 (the cold sore version of herpes) but you probably already have that. Oral-anal contact ('rimming') is a good way to catch various nasties, including HepB and HepA.
Ultimately, the decision is down to you - if you absolutely do not want to catch anything, do not do OWO. If you do OWO, make sure your throat gets checked out when having your regular sexual health checks because most of the STIs often don't have any symptoms there.
Topic: Risks from OWO (Read 409251 times)