We analysed the potential influence of hepatitis C virus (HCV) co-infection over IL-7 levels and thymic function in naive HIV-infected patients and after effective HAART. HIV-HCV-co-infected patients had lower plasmatic IL-7 levels compared with HIV-monoinfected patients. This effect may not be associated either with HCV monoinfection or with the rate of liver injury. These lower levels may explain, at least partly, the lower CD4 cell repopulation of HIV-HCV-co-infected patients after HAART.