Background-Bipolar and substance use disorders frequently co-occur, and both are associated with impulsivity, impaired judgment, and risk-taking.Objectives-This study aimed to: (1) describe the rates of HIV sexual and drug risk behaviors among patients with co-occurring bipolar and substance use disorders, (2) test whether acute mania, psychiatric severity, and drug severity independently predict HIV risk, and (3) examine the relationship between specific substance dependencies and sexual risk behaviors.Method-Participants (N = 101) were assessed for psychiatric diagnoses, substance abuse, and HIV risk behavior using structured clinical interviews and self-report questionnaires.Results-The majority (75%) were sexually active in the past 6 months and reported high rates of sexual risk behaviors, including unprotected intercourse (69%), multiple partners (39%), sex with prostitutes (24%, men only), and sex trading (10%). In a multivariate linear regression model, recent manic episode, lower psychiatric severity, and greater drug severity were independent predictors of total HIV risk. Cocaine dependence was associated with increased risk of sex trading.Conclusions-Results underscore the importance of HIV prevention for this population.