In order to investigate the prevalence of antibody to hepatitis C virus (anti-HCV) in renal transplant patients, the evolution of anti-HCV status, and clinical outcome in anti-HCV-positive renal allograft recipients, we tested the sera from 120 renal transplant patients for anti-HCV. Thirty-eight patients were hepatitis B surface antigen (HBsAg)-positive. Two patients were anti-delta-positive. A total of 79 patients (65.8%) had at least one serum positive for anti-HCV. Anti-HCV positivity decreased after transplantation for more than 5 years (65.5% at transplantation versus 37.9%, 78.3 +/- 13.4 months later). Among those with positive anti-HCV, the HBsAg-positive group had significantly higher incidence of chronic hepatitis (50% vs. 25.5%, P = 0.026) and liver cirrhosis (21.4% vs. 0%, P = 0.001) than HBsAg-negative group. Among the 82 HBsAg-negative patients, the prevalence of anti-HCV was significantly higher in those with chronic hepatitis than in those without (86.7% vs. 56.7%, P = 0.027). We conclude from this study: (1) anti-HCV positivity is quite prevalent in renal transplant patients; (2) coinfection of hepatitis B virus (HBV) and hepatitis C virus (HCV) may lead to aggressive liver disease and cirrhosis; HCV infection alone has a more benign clinical outcome; and (3) HCV infection is an important cause of posttransplant chronic hepatitis in HBsAg-negative patients.