In a retrospective survey of patients hospitalized in the Department of Medicine of the University Hospital, Basel, Switzerland, from 1980 to 1986, we found 269 patients with history of past or current drug abuse. The charts of these patients were analyzed for infectious complications according to defined criteria. Heroin was the principal drug consumed by 95%. In 127patients (47%) at least one infectious complication was diagnosed. In 125(31%) of 404 admissions, the infectious problem was the main reason for hospitalization. Among the 269 patients, 217 infective episodes occurred. Pulmonary infections were the most frequently occurring (52 episodes). There were 44 cases of viral hepatitis, 30 of human immunodeficiency virus infection, and 25 of minor genital infections. Bone and joint infections and sepsis/endocarditis werediagnosed in seven cases each. The overall mortality was 4.1%; however, only three of the 11 deaths were attributed to infections. Intravenous drug addiction is complicated by a high morbidity because of infections that were seldom lethal during the observed period.