The dual risks of male-to-male sex and drug injection have put men who have sex with men and inject drugs (MSM-IDU) at the forefront of the HIV epidemic, with the highest rates of infection among any risk group in the United.States. This study analyzes data collected from 357 MSM-IDU in San Francisco between 1998 and 2002 to examine how risk behaviors differ by HIV serostatus and self-identified sexual orientation and to assess medical and social service utilization among HIV-positive MSM-IDU. Twenty-eight percent of the sample tested HIV antibody positive. There was little difference in risk behaviors between HIV-negative and HIV-positive MSM-IDU. Thirty percent of HIV-positive MSM-IDU reported distributive syringe sharing, compared to 40% of HIV negatives. Among MSM-IDU who reported anal intercourse in past 6 months, 70% of positives and 66% of HIV negatives reported unprotected anal intercourse. HIV status varied greatly by self-identified sexual orientation: 46% among gay, 24% among bisexual, and 14% among heterosexual MSM-IDU. Heterosexual MSM-IDU were more likely than other MSM-IDU to be homeless and to trade sex for money or drugs. Gay MSM-IDU were more likely to have anal intercourse. Bisexual MSM-IDU were as likely as heterosexual MSM-IDU to have sex with women and as likely as gay-identified MSM-IDU to have anal intercourse. Among MSM-IDU who were HIV positive, 15% were currently on antiretroviral therapy and 18% were currently in drug treatment, and 87% reported using a syringe exchange program in the past 6 months. These findings have implications for the development of HIV interventions that target the diverse MSM-IDU population.