To assess the epidemiology of hepatitis C virus (HCV) in Poland, anti-HCV was studied in patients with acute and chronic non-A, non-B (NANB) hepatitis, in healthy adults, and in subjects at risk. Anti-HCV prevalence was 2 % in 152 blood donors, 78 % in 95 parenteral drug addicts, 21 % in 112 alcoholics, and 86 % in 42 patients with chronic NANB hepatitis. Among 34 prospectively followed patients with acute NANB hepatitis 17 (50%) developed anti-HCV. It seems that HCV infection is responsible for the majority of NANB hepatitis in Poland and is common in parenteral drug abusers and alcoholics.