Clinical and necropsy findings in 13 intravenous drug abusers who died of the acquired immunodeficiency syndrome (AIDS) were reviewed and compared with findings in eight patients who acquired the infection through sexual exposure, the most common mode of transmission in AIDS. No differences were found in lymphocyte counts or duration of survival, despite reports that the degree of immunosuppression in intravenous drug abusers with AIDS differs from that in homosexuals. Neoplasms were found in 25 per cent of patients with sexual risks, but not in any drug abusers (0 per cent). Two opportunistic infections (toxoplasmosis and cytomegalovirus pneumonia and esophagitis) were more common in the intravenous drug abuser group. Although cytomegalovirus has been associated with Kaposi's sarcoma, this association was not found in this study. The postmortem findings in both groups were otherwise similar.