SummaryHuman immunodeficiency virus (HIV)-infected gay and bisexual men (n = 609) randomly selected from two HIV outpatient clinics in Los Angeles completed confidential, self-administered questionnaires at the clinics, reporting sexual activities and disclosure during the previous 2 months. Approximately 9% had engaged in unprotected insertive anal intercourse with one or more partners. This activity was 3.27 times more likely to have occurred with seropositive partners than with partners who were seronegative or whose serostatus was unknown. Fourteen men (2.3% of total sample) had engaged in unprotected insertive anal sex with 25 seronegative or unknown serostatus partners who were not informed of their risk of infection. Thirty-three men (5.4% of total sample) had engaged in this activity with 37 seropositive partners who were informed. Clinicians and other health professionals can play an important role in helping to control the HIV epidemic by discussing with seropositive patients the importance of using safer sex and informing sexual partners. Such discussion should include information about the potentially negative health effects of unprotected sex between seropositive persons.