Introduction and Aims: The number of illicit drug users incarcerated in Sri Lanka has been growing over the last decade. This paper presents drug-use characteristics and risk-taking behaviours among a group of male incarcerated drug users. Design and Methods: An interviewer-administered structured questionnaire was completed by 278 drug users in three prisons in Sri Lanka. Results: The majority (81.3%) of interviewees were aged 25-45 years. Most of them had received low levels of education, and experienced childhood delinquency and a deprived upbringing. Drug use was largely initiated during early adolescence, then continued to chronicity and the development of drug dependence. There was a high incidence (25-35%) of family history of drug abuse. Heroin (98%) and cannabis (54%) were the main drugs of abuse in the past 30 days. Polydrug use was common (75% in the past 12 months). Tobacco and alcohol use were widespread. The prevalence of intravenous drug use was higher than officially reported (15.8% vs. 1%). There was a high prevalence (53%) of risk-taking sexual behaviour. Discussion and Conclusion: The pattern of drug use was similar to those reported in nearby countries. However, the increasing prevalence of injecting drug use and risk-taking sexual behaviour is a concern. There is an urgent need to develop effective treatment strategies and to prevent the spread of HIV and hepatitis in Sri Lanka.