Intravenous drug use, sexual promiscuity and a longer cohabitation period are considered risk factors for familial transmission of hepatitis C virus. The relative importance of this type of transmission is a subject of controversy. Aim: To study familial clustering of hepatitis C virus infection and its risk factors. Material and methods: HCV positive patients (91 with chronic hepatitis, 88 with cirrhosis, nine with hepatic carcinoma and 29 hemophiliacs) were the index cases. HCV antibodies were measured by ELISA and the type of relationship with the index case was investigated in 317 family members. Results: Positive anti HVC antibodies were detected in 12 of 243 family members of patients with chronic liver disease and in none of the family members of patients with hemophilia. Of these, five were couples of an index case with a long cohabitation period. Ten members had an index case with a severe liver disease (three with Child C cirrhosis and seven with liver carcinoma). Conclusions: Family transmission of HCV infection is uncommon in Chile. The association of severe liver disease and family transmission could be due to a higher viral load as responsible for transmission during the early periods of a long lasting disease (Rev Méd Chile 2003; 131: 1123-27).