Objective: The effects of hepatitis C virus (HCV) coinfection on immune homeostasis and immune restoration in treated HIV infection are not well understood. Methods: We studied 79 HIV-infected patients who had been receiving HAART for more than 2 years and who had HIV viral load below 50 copies/ml. Four patient groups were studied: HIV+/HCV+, CD4+ cells above 350/μl; HIV+/HCV+, CD4+ cells below 350/μl; HIV+/HCV-, CD4+ cells above 350/μl; HIV+/HCV-, CD4+ cells below 350/μl. Controls comprised 20 healthy volunteers. Naive, central memory, effector memory, and terminal effector CD4+ T cells were enumerated. Naive CD4+ CD31+ T cells were counted as recent thymic emigrants (RTEs). Activation state and ex-vivo apoptosis of CD4+ T cells, levels of liver enzymes, and aspartate aminotransferase-to-platelet ratio index were evaluated. Results: CD4+ T-cell counts and the numbers of all circulating CD4+ T-cell maturation subsets were diminished in HIV infection; CD4+ T-cell activation and apoptosis were increased in HIV infection, but none of these indices was affected by HCV coinfection...