GB virus type C is a well-known viral agent with capability of infecting patients undergoing hemodialysis. Liver enzyme levels in infected individuals have been reported to remain within the normal range. Simultaneous infection of GBV-C and other viral agents may occur due to common routes of transmission. A total of 104 hemodialysis patients living in Tehran were included in this case-control study (53 patients with HCV infection, group I; and 51 with no HCV infection, group II). Diagnosis was made by detection Anti-E(2) protein using ELISA and HCV-RNA using RT-PCR. History of HBV-infection, organ transplantation, depression, malignancies, chemotherapy, diabetes mellitus, thyroid disorders and chronic cutaneous disorders were considered. Patients were evaluated for high- risk behaviors such as intravenous drug injection, addiction or substance abuse. A total of 14 patients (13.6%) were GBV-C-infected. Four of them were co-infected with HCV. All patients with GBV-C infection had viral genotype 2. Thirteen patients (12%) had a history of multiple blood transfusions. Mean (+/-SD) age of GBV-C-infected patients was 48.7+/-13.8 years. Among GBV-C infected patients, three patients had a history of organ transplantation and three had a co-morbidity of diabetes mellitus. This study as the first case-control study to evaluate the association between GBV-C and HCV infection, to our knowledge, shows hemodialysis patients living in Tehran are infected with GBV-C with intermediate level of frequency. The association of GBV-C transmission with other viral blood-borne agents might be necessary.