This paper reports an outcome evaluation and needs assessment conducted by the AIDS and Substance Abuse Program (ASAP) of the San Francisco AIDS Health Project. The study was designed to: 1) evaluate effectiveness of a hospital based intervention and referral service for HIV affected substance abusers, and 2) gather information from this population regarding accessibility and barriers to drug treatment. Participants were 86 individuals consecutively referred to ASAP over an 8-month period. All received a brief needs assessment interview in addition to the standard ASAP evaluation protocol. Agency follow-up contacts were made for those individuals referred by ASAP to extended substance abuse treatment, with information limited to whether or not the client contacted the designated referral resource. Source of referral to ASAP, interest in treatment, and prior sexual risk behavior change were significant predictors of intervention outcome. Personal unreadiness and treatment program waiting lists were the most frequently reported obstacles to treatment. While most participants reported changing risk behavior in response to the AIDS epidemic, patterns of change differed according to intravenous drug use history.