Having unprotected (sex without a condom) sexual intercourse (vaginal or anal) with someone who has HIV.

Having unprotected oral sex with someone who has HIV. The risk goes up if there is ejaculation in the mouth. The risk rises still higher if either partner has cuts or sores in the mouth from recent tooth brushing, bleeding gums, canker sores or other sexually transmitted diseases (STDs).

Sharing needles or syringes with someone who is HIV infected.

Sharing needles, syringes or drug works with someone infected with HIV.

Pregnancy, childbirth or breast-feeding if the mother has HIV infection.