To examine the risk factors of HIV type-I infection among male drug addicts in Malaysia, a case-control study was conducted on inmates, aged 20-40 years, at a drug rehabilitation centre in January, 1994. Stratified random sampling was performed. A total of 87 cases and 261 controls, chosen by frequency matching for age and ethnicity, answered self-administered questionnaires. About 59.8% of the subjects administered drugs intravenously and of these, 71.2% shared needles. Practices significantly associated with HIV infection were needle-sharing (OR = 8.53; 95% CI = 3.36-5.52), sexual relationship with prostitutes (OR = 3.70; 95% CI = 2.10-6.56), homosexuality (OR = 4.05; 95% CI = 1.49-11.11) and non-condom use while having sex with prostitutes (OR = 2.27; 95% CI = 1.05-4.97).