Persistent coinfection with the apathogenic GB virus C (GBV-C) is associated with slower disease progression of human immunodeficiency virus (HIV)-1 infection. Aim of this study was to investigate whether Fas plays a role in this beneficial effect. Fas expression and susceptibility to Fas-mediated apoptosis (FMA) was analyzed in peripheral blood mononuclear cells (PBMCs) of HIV-1 patients coinfected and non-coinfected with GBV-C. Fas expression and function was evaluated in 42 GBV-C coinfected and 101 non-coinfected HIV-1 patients. Thirteen healthy and 11 Hepatitis C virus (HCV)-monoinfected individuals were analyzed as controls. Cell surface Fas expression was determined by flow cytometric analysis. Apoptosis was evaluated by staining with Annexin V and Viaprobe followed by multiparameter flow cytometry analysis. In untreated HIV-1 patients GBV-C coinfection was associated with significantly lower percentage of Fas expressing cells as compared to GBV-C non-coinfected individuals. Expression of Fas was directly correlated with sensitivity to Fas-mediated apoptosis. Sensitivity to FMA was unchanged in GBV-C coinfected patients. PBMCs of patients receiving highly active antiretroviral therapy (HAART) did not show such a difference. Untreated HIV-1 patients with GBV-C coinfection have reduced cell surface Fas expression. Lower FMA of T-cells might contribute to prolonged survival of GBV-C coinfected HIV-1 patients.