AIM: To determine the pathogenicity of GB virus C (GBV-C) on liver and the effects of its co-infection on the clinical features and prognosis of patients with hepatitis B and C. METHODS: Cross-sectional study was carried out in 413 patients with acute, chronic hepatitis B or liver cirrhosis, and in 67 hemodialysis patients. A 20-month prospective cohort study was carried out in 95 hepatitis B and 80 hepatitis C patients. A reverse transcriptase nested polymerase chain reaction (RT-nPCR) of the 5'-noncoding region was used to detect circulating GBV-C RNA. Liver function was determined by an automated analyzer for all patients. RESULTS: The prevalence of GBV-C in the high-riskpopulations with the virus transmitted via blood was high, ranging from 16.2 to 28.8%. Co-infection with GBV-C in hepatitis B patients did not affect the clinical features of the disease or liver function. The dialysis patients infected with GBV-C alone did not develop functional changes to the liver. Prospective cohort study showed that GBV-C co-infection did not affect the clinical features, prognosis or negative serum conversion rate of chronic hepatitis B and C. CONCLUSION: The results suggest that GBV-C has no marked pathogenicity on liver, so it may not be a hepatitis virus.