Summary. Coinfection with GBV-C/HGV in patients with chronic hepatitis C (CHC) may influence clinical course and response rates of antiviral therapy. Aim of the study was to investigate the prevalence of GBV-C/HGV/HCV coinfection and its influence on outcome of interferon/ribavirin combination therapy. Three hundred and four patients with CHC [m/f = 211/93, age: 42 (18-65)] were investigated. HGV RNA detection was performed by polymerase chain reaction prior to and 6 months after the end of antiviral therapy. HGV/HCV coinfection could be identified in 37/304 (12.2%) patients with intravenous drug abuse as the most common source of infection (N = 21, (56.8%)). The predominant HCV genotype in coinfected individuals was HCV-3a (HCV-3a: 51.4%, HCV-1: 37.8%, HCV-4: 10.8%). HGV coinfection was more prevalent in patients infected with HCV-3 compared to HCV-1 or HCV-4 [19/45 (42.2%) vs 14/185 (7.6%) vs 4/52 (7.7%), P < 0.01]. Patients with HGV/HCV coinfection were younger [35 (18-56) vs 43 (19-65), years; P < 0.01], and advanced fibrosis (F3-F4) was less frequent (22.2%vs 42.9%, P < 0.05). A sustained virological response was achieved more frequently in HGV/HCV coinfected patients [26/37 (70.3%)] than in monoinfected patients [120/267 (44.9%), P < 0.01]. HGV RNA was undetectable in 65.7% of the coinfected patients at the end of follow-up. Intravenous drug abuse seems to be a major risk factor for HGV coinfection in patients with chronic hepatitis C. Coinfection with HGV does not worsen the clinical course of chronic hepatitis C or diminish response of HCV to antiviral therapy. Interferon/ribavirin combination therapy also clears HGV infection in a high proportion of cases.