GB virus C (GBV-C) infection is frequent in patients infected with the human immunodeficiency virus (HIV) due to similar transmission routes of these viruses. The aim of this study was to determine the rate of infection and genotypic characteristics of GBV-C in this population. The presence of GBV-C RNA was determined in serum samples of 106 patients infected with HIV by reverse transcriptase-nested polymerase chain reaction. GBV-C genotypes were determined by direct sequencing. Hepatitis B surface antigen (HBsAg), hepatitis B surface antibody (anti-HBs), hepatitis C antibody (anti-HCV), alanine aminotransferase (ALT) levels, HIV viral load and CD4(+) count were also tested in all patients. The overall prevalence of GBV-C infection was 11.3% in HIV patients. There was no significant difference between patients with and without GBV-C infection regarding age, sex, route of transmission, viral load, ALT levels, HBV and HCV co-infection and treatment with antiretroviral drugs. 66.7% of patients with GBV-C had a CD4(+) count > or = 200 and 33.3% had a CD4(+) count < 200 cells/mm(3). Phylogenetic analysis revealed that all GBV-C isolates were genotype 2, and classified as subtype 2a. GBV-C infection is relatively common in patients infected with HIV. The prevailing GBV-C genotype 2a in this study group concurred with reports from other parts of the Middle East.