Objective: Risky sexual behaviour among drug users is a major concern due to the spread of HIV and hepatitis. We investigated correlates of risky sexual behaviour in incarcerated drug users in Sri Lanka. Methods: A structured questionnaire was administered by interviewer to 278 Sinhalese speaking male prisoners charged with illicit drug use. Participants also completed the AUDIT, Sexual Disorder Screening (SDS), Behavioural Inhibition System/Behavioural Activation System (BIS/BAS) and Sensitivity to Punishment/Sensitivity to Reward Questionnaire (SPSRQ) measures to assess substance use patterns and personality traits. Selected demographics, father’s substance abuse pattern, polydrug use, intravenous (IV) drug use, childhood sexual abuse, AUDIT, SDS and personality scores were entered using backward multivariate logistic regression to analyze predictors of sexual promiscuity, sex with commercial sex workers (CSW) and homosexual behaviour. Results: Polydrug use, IV drug use and SDS score were predictors of sexual promiscuity and having sex with CSW. Low AUDIT score and low educational background were predictors of sexual promiscuity. Predictors of homosexual behaviour included IV drug use, SSS, and BAS fun-seeking score. Conclusion: Consistent with previous studies, IV drug use and polydrug use were significant predictors of unsafe sexual behaviour among drug users. Impulsive personality traits were strong correlates of risky sexual behaviour in drug users. Early screening programs for these risk factors would be beneficial to prevent risky sexual behaviour among drug users.