The purpose of this study was to assess associations between substance use (alcohol to intoxication, heroin, and cocaine) and sexual activity, high risk sexual behaviors, and STD among detoxification inpatients (n = 470). Participants were surveyed on past 30 day substance use, past 6 month sexual behaviors, and STD in the past 6 months and/or over 24 months of follow-up. Logistic regression models adjusted for demographics found that cocaine use was significantly associated with being sexually active (OR(adj) = 2.3, 95% CI = 1.1-4.8) and selling sex (OR(adj) = 2.6, 95% CI = 1.3-5.3). Alcohol and heroin were not significantly associated with sexual activity, high risk sexual behaviors or STD in this sample.