This is a question you’ll get asked exhaustively (see Disclosure: Here’s How for advice on how to deal with it), but right now you’re probably just asking yourself. The bottom line is that the main risk is having unprotected anal sex or (for women) vaginal sex or sharing needles with an infected person. It’s possible, but quite a bit less likely, that you got it from oral sex. The CDC says it’s also possible to acquire HIV through exposure to infected blood, transfusions of infected blood, blood products, or organ transplantation, “though this risk is extremely remote due to rigorous testing of the U.S. blood supply and donated organs.”