This investigation was carried out on 851 consecutive judicial autopsies of drug addicts who died mostly of heroin overdose from 1977 to 1996. Research of anti-HIV/HBV/HCV antibodies was performed, and histologic sections were retrospectively reviewed. More than 65% were HBV/HCV-positive and about 17% HIV-positive; females were HIV-positive more often than males. Intracranial microhemorrhages were frequently found; cerebral infectious diseases were rare. Inflammatory heart lesions, myocardial fibrosis, and acute ischemia were common. Interstitial nephritis (found in about 8%) was more frequent in females, in older patients, and in those carrying HIV infection; glomerular sclerosis was detected in about 12%. Acute bronchitis and/or pneumonia was demonstrated in 12%, without significant association with HIV infection; pulmonary hemorrhages, foreign body granulomas, and food aspiration were also commonly seen; hyperplasia of pulmonary perivascular lymphatic tissue was rather characteristic. Liver was carrying steatosis in 66.3% and/or hepatitis in 64.5%; acute hepatitis was more frequent in females, chronic hepatitis in older subjects and in those proven positive for hepatotropic viruses; cirrhosis occurred more often in older patients, in those carrying virus infection, and in consumers of nonnarcotics drugs such as ethanol. No pathologic finding was clearly related to drug abuse; therefore, during autopsy, drug addiction can be suspected, but anamnestic and circumstantial data are needed to lead pathologists to request toxicologic analysis to ascertain the cause of death. The present investigation emphasizes that, in addition to the risk of death by overdose, the high incidence of acute and chronic diseases could seriously undermine the health status of heroin and/or other drug consumers.