The spread and genotypical variability of GBV-C virus were determined among the HIV-positive patients in the Russian Federation. More than a fourth (26.2%) of the HIV-infected patients were shown to have GBV-C coinfection; all virus isolates belonged to genotype 2 with a predominance of subtype 2a. Analysis of the impact of GBV-C coinfection on HIV burden and CD4 lymphocyte levels showed no significant impact on these basic characteristics of HIV infection. However, coinfection with GBV-C and HIV was associated with the higher frequency of undetectably low (