This study examined the relationships between hepatitis C virus (HCV) genotypes and the routes of HCV transmission in 101 patients with chronic hepatitis C. Patients who received blood transfusions (43%) and those with chronic hepatitis C of unknown cause (37%) had similar mean ages, age distribution, and HCV genotype distribution (1a, 19% vs. 14%; 1b, 52% vs. 54%; 3a, 10% vs. 9%; other, 19% vs. 23%). Intravenous drug users (IVDUs) were significantly younger and had a different genotype distribution (1a, 33%; 1b, 0; 3a, 63%; other, 5%; P < .001). Transmission of HCV 3a has been observed only over the past 20 years; other genotypes were transmitted up to 40 years ago. These results suggest that for 20 years there have been two independent ongoing hepatitis C epidemics. One affects persons who received blood transfusions or whose source of infection is unknown. These persons are older and are mainly infected by HCV 1b. The second type of infection occurs in IVDUs and infects younger persons, mainly with HCV 3a.