Summary: A cross-sectional study was undertaken to determine the clinical profile, haematological and biochemical changes, seroprevalence of common opportunistic pathogens, and AIDS-defining events in 49 Malaysian male drug addicts with HIV infection. Their mean age was 33.2 years, the majority had been injecting drugs for more than 5 years and 88% reporting sharing needles. Fatigue, weight loss and night sweats were common presenting symptoms and the most frequent physical findings were hepatomegaly (57%), lymphadenopathy (35%) and thrush (29%). Pulmonary infections were the commonest complications seen (61%) and of these, 13 had septic pulmonary emboli, 7 had bacterial pneumonias, 7 had pulmonary tuberculosis, and 4 had Pneumocystis carinii pneumonia. Eight patients had infective endocarditis and 5 had infected pseudoaneurysm in the groin. Anaemia (82%), leucocytosis (53%), hypoalbuminaemia (43%), hyperglobulinaemia (88%), elevated liver enzymes and hyponatraemia (57%) were frequent laboratory findings. The prevalence of HCV, HBV, cytomegalovirus and toxoplasma infection (by serology) were 100%, 12.2%, 72.7% and 59% respectively. All 7 patients with AIDS (4 P. carinii pneumonia, 2 extrapulmonary tuberculosis, and one oesophageal candidiasis) presented with their AIDS-defining illness, suggesting that HIV-infected intravenous drug user (IVDU) patients present late in the course of the disease.