Abstract: The epidemological and clinical features of hepatitis C virus infection have been evaluated in a cohort of 227 intravenous drug users enrolled at a drug dependence treatment center in the Veneto area in 1992–1993 and followed periodically. Hepatitis C virus infection was detected using second-generation anti-HCV ELISA in 171 (75%) subjects at enrollment. Anti-HCV seropositivity correlated with: a) the duration of drug abuse: 91% of intravenous drug users injecting for more than 8 years were seropositive as compared to 40% of those with a history of abuse lasting 4 years or less, p<0.001; b) sharing of injection equipment: 85% anti-HCV positive intravenous drug users had shared at some time as compared to 64% seronegative subjects, p<0.001; c) seropositivity for immunodeficiency virus infection: 25% anti-HCV positive intravenous drug users were coinfected as compared to 3.5% anti-HCV negative, p<0.001; d) markers of ongoing (two cases) or previous hepatitis B virus infection were detected in 62% of anti-HCV positive but in 21% of anti-HCV negative cases, p<0.01. Two initially anti-HCV negative intravenous drug users seroconverted during follow up giving an incidence rate of hepatitis C virus infection of 6.2 per 100 person-years. During the survey abnormal alanine aminotransferase levels were detected in 75% anti-HCV positive but in 24% anti-HCV negative cases (p<0.001), with significantly higher levels in the former. These findings suggest that the circulation of hepatitis C virus among intravenous drug users has been decreasing in recent years, although new infections still occur. In agreement with the high rate of chronicization of parenterally transmitted hepatitis C, the majority of anti-HCV positive subjects had biochemical features of associated liver disease.