This study examined the prevalence and correlates of sexual risk behaviors and sexually transmitted infections (STIs) in two samples of outpatients with borderline personality disorder (BPD), including suicidal BPD women (n = 99) and opiate-dependent BPD men and women (n = 125). High rates of sexual risk behaviors and STIs were found, particularly in the opiate-dependent BPD sample. Compared with suicidal BPD outpatients, opiate-dependent BPD outpatients reported higher rates of past-year sexual activity, commercial sex work, and lifetime hepatitis, as well as a greater number of lifetime sex partners. Substance use and demographic characteristics (age, sex, and marital status) were associated with higher rates of sexual risk behaviors and/or STIs, whereas cognitive-behavioral factors and indicators of psychiatric impairment were not. These findings point to a clear need for interventions aimed at decreasing sexual risk behaviors among individuals with BPD.