Background/Aims: Recently, the hepatitis GB-C virus (GBV-C) has been identified as another virus potentially causing chronic hepatitis, Although high rates of coinfection are emerging in drug addicts with chronic hepatitis C virus infection, no detailed data on clinical presentation are available, Therefore, co-infection was sought in hepatitis C virus patients to determine the impact of GB-C virus on clinical presentation. Methods: GBV-C was determined by nested reverse transcriptase-polymerase chain reaction in serum of 70 HIV negative intravenous drug abusers with chronic hepatitis C, Biochemical, histological and virological parameters were compared between patients with or without GBV-C coinfection. Results: Hepatitis C virus and GBV-C coinfection was found in 18 of 70 (25.7%) patients, Cases with coinfection were younger and had shorter duration of disease (31.4 +/- 6.2 vs, 35.3 +/- 7.3 (p = 0.09) and 9.9 +/- 6.8 vs, 12.9 +/- 7.7 (p = 0.17) years) than those without coinfection, Neither hepatitis C virus genotype distribution and HCV RNA levels nor serum liver function tests, titers of immunoglobulins or autoantibodies differed between the two groups, Histologically, chronic active hepatitis (16.7 vs, 46.4%, p = 0.07), fibrosis (8.3% vs, 21.4%, p = 0.3), and cirrhosis (0% vs. 8.2%, p = 0.31) were less prevalent in coinfected patients, After interferon treatment, 5/6 coinfected and 11/19 patients with hepatitis C virus infection alone had cleared HCV RNA and 4/6 lost GBV-C RNA from serum, The two patients with GBV-C/HCV infection who persistently cleared hepatitis C virus but not GBV-C from serum had normal transaminases during follow-up despite persistence of GBV-C. Conclusions: Coinfection of chronic hepatitis C patients with GBV-C does not lead to a significant change in clinical presentation, severity of liver disease, hepatitis C viremia, or response to interferon treatment.