Hepatitis C virus (HCV) is the most common cause of chronic liver disease in patients with end-stage renal disease. It is more prevalent in hemodialysis (HD) patients than the general population but the exact routes of transmission are not clear. In this study, the current situation of HCV infection was assessed in eleven dialysis centers in Tehran, Iran. A total of 548 patients on maintenance HD with a mean age of 45.4 +/- 16.8 years were studied. Most of the patients were dialysed 3 times/week, each session lasting 4 to 4.5 hours. About 15% of patients had a history of having received peritoneal dialysis prior to maintenance HD and 23.6 of patients had received blood transfusion(s). The most common cause of renal failure was hypertension in 29.7% followed by diabetes mellitus in 23.2%, failed renal transplant in 19.4% and glomerulonephritis in 9.7%. HCV antibodies were measured by ELISA-III. All positive sera were tested for HCV RNA by RT-PCR. Positive HCV antibody tests were present in 19.6% of patients. In these seropositive patients, 48.6% had detectable HCV RNA. Prevalence of HCV antibody seropositivity was not different in patients with or without history of blood transfusion. The prevalence of positive HCV antibody in this study was higher than reports from Europe but lower than other countries in the region. Only 48.6% of seropositive cases were confirmed by PCR, which is lower than expected values. It seems that nosocomial transmission is the main route of infection in Iran.