Although hepatitis G virus infection (HGV) is usually asymptomatic, it has been associated with mild hepatic injury. Whether hepatitis G co-infection alters the natural history of other viral hepatitis infections remains to be determined. In the present study, we investigated whether hepatitis G impacts on the time to recurrent hepatitis or on the time to progression to fibrosis in hepatitis C-infected patients who undergo liver transplantation. Forty-five liver transplantation recipients with persistent hepatitis C viremia by polymerase chain reaction (PCR) were evaluated. Stored sera obtained before and after liver transplantation was tested for HGV RNA by reverse transcriptase (RT)-PCR using primers to the 5' region of the HGV genome. A median of eight serial liver biopsy specimens were reviewed per patient. The prevalence of HGV co-infection was 21% before transplantation and 22% following transplantation. During a median follow-up of 29 months, 78% (35/45) of patients with hepatitis C viremia developed histological features of recurrent hepatitis. Fifty-one percent (23/45) progressed to fibrous portal expansion and 16% (7/45) developed bridging fibrosis. Comparisons of patients with and without hepatitis G co-infection following transplantation showed no significant difference in time to recurrent hepatitis, fibrous portal expansion, bridging fibrosis, or of allograft or patient survival. In conclusion, hepatitis G co-infection does not seem to impact on the time to recurrent hepatitis C or progression of hepatitis C-related histological injury after liver transplantation.