The abuse by injection of heroin or other drugs has long been associated with liver disease caused by hepatitis B virus (HBV) and other viruses. Increasingly severe hepatic and virological complications of parenteral drug abuse have been reported due to infection with new viruses or concomitant alcohol abuse. The hepatitis delta virus (HDV) can replicate and cause liver infection only in the presence of HBV; such infection in HBV carriers may cause rapidly progressive and clinically significant liver disease. Liver cirrhosis is frequently detected in parenteral drug abusers who have chronic infection with both HBV and HDV or who also abuse alcohol.