A large seroepidemiologic and genotyping study of hepatitis C virus (HCV) was conducted in Lima, Peru, during the periods of 1986 to 1993 (cohort A) and 1994 (cohort B). Anti-HCV seroprevalence rates were 15.6% (216 of 1,389) and 11.7% (168 of 1,438), respectively. Low rates were seen among volunteer blood donors (1.1% and 0.8%). Anti-HCV rates were much higher among patients undergoing hemodialysis (43.7% and 59.3%), hemophiliacs (60.0% and 83.3%), in those more than 39 years old (18.2% and 26.0%), in females (25.0% and 27.4%), and in less-educated persons (16.9%). Age- and gender-adjusted risk factors in cohort B included blood transfusion history (adjusted odds ratio [AOR] = 29.8), prior organ transplantation (AOR = 9.1) or a history of hepatitis (AOR = 4.9), previous hospitalization (AOR = 3.7), a history of intravenous drug use (AOR = 3.5), prior major surgery (AOR = 2.6), a history of acupuncture (AOR = 2.1), previous dental procedures (AOR = 1.2), and prior medical injections (AOR = 1.04). The most prevalent HCV genotype was type 1 (86%), followed by type 3 (10%) and type 2 (2%). Transmission through unsafe injection-related and medical/dental procedures appears to play an important role in HCV infection among Peruvians.