OBJECTIVE Hepatitis G virus (HGV) is transmissible by blood transfusion, but its role in chronic liver disease is unknown. The aim of this study was to determine the prevalence of HGV infection in patients infected with hepatitis C virus (HCV) undergoing transplantation and evaluate the effects of HGV coinfection on the course of posttransplantation HCV infection. METHODS One hundred twenty-four patients infected with HCV undergoing liver transplantation were studied. Serum samples were tested for HCV and HGV RNA; HCV RNA was quantitated by branched DNA assay, and HCV genotype was determined. RESULTS The prevalence of pretransplantation and posttransplantation HGV infection was 24% and 28%, respectively. Pre-transplantation HGV infection was positively correlated with posttransplantation HGV infection (P < 0.001). Pretransplantation clinical features were not different in patients infected with HCV with and without HGV infection. Posttransplantation HCV RNA levels were not significantly different in patients with and without HGV coinfection, but HCV genotype 1b was more frequent in patients with HGV coinfection. There were no differences in the histological severity of posttransplantation liver disease, graft, and patient survival between patients with and without HGV infection. CONCLUSIONS Although HGV coinfection is frequent in patients with end-stage HCV disease undergoing liver transplantation, there is no association between the presence of HGV coinfection and the severity of liver disease post-transplantation, graft, or patient survival.