Objective. To assess HIV vaccine acceptability among high-risk adults in Los Angeles. Study Setting. Sexually transmitted disease clinics, needlesyringe exchange programs, Latino community healthHIV prevention programs. Study Design. Cross-sectional survey using conjoint analysis. Participants were randomly selected using three-stage probability sampling. Data Collection. Sixty-minute structured interviews. Participants rated acceptability of eight hypothetical vaccines, each with seven dichotomous attributes, and reported post-vaccination risk behavior intentions. Principal Findings. Participants (n=1164; 55.7 percent male, 82.4 percent ethnic minority, mean age=37.4 years) rated HIV vaccine acceptability from 28.4 to 88.6; mean=54.5 (SD=18.8; 100-point scale). Efficacy had the greatest impact on acceptability, followed by side effects and out-of-pocket cost. Ten percent would decrease condom use after vaccination. Conclusions. Findings support development of social marketing interventions to increase acceptability of "partial efficacy" vaccines, behavioral interventions to mitigate risk compensation, and targeted cost subsidies. © Health Research and Educational Trust.