Objective: The objective of this study is to evaluate the impact of hepatitis C virus (HCV) serostatus on the evolution of CD8 þ cells and CD4 þ : CD8 þ ratio in HIV-infected patients on combined antiretroviral therapy (cART) who achieve sustained undetectable viral load (HIV-pVL). Design and methods: A longitudinal study performed in an outpatient HIV-unit following 1495 HIV-infected patients. Data of patients on cART achieving undetectable HIV-pVL for at least 3 years were collected retrospectively from our medical e-database NADIS from January 1997 to April 2005, a period defined in order to select patients who were naive of hepatitis treatment. T-cell counts were assessed every 6 months from HIVsuppression over the study period. Results: Two hundred and twenty-six HIV mono-infected (group 1) and 130 HCVcoinfected patients (group 2; genotype prevalence: 42% HCV-G1, 26% HCV-G3, 11% HCV-G4 and 21% HCV-G2) fulfilled the selection criteria. cART regimens were comparable between the groups, as were CD4 þ and CD8 þ cell counts at the first undetectable HIV-pVL. After 3 years, both groups displayed similar CD4 þ cell reconstitution, although CD4 þ percentage was higher in group 1 (30.3 AE 1.1 vs. 27 AE 1.1%; P < 0.001). HIV suppression led to a significant drop of median CD8 þ cell counts in group 1 (P ¼ 0.027), but not in group 2, which displayed higher CD8 þ cell counts all through the follow-up (mean diff. ¼ 135.71 AE 26.89 cells/ml, P < 0.001). Moreover, the fraction of patients reaching CD4 þ : CD8 þ ratio ! 1 was lower in group 2 (14 vs. 27.7%; P < 0.05). Conclusion: Despite sustained HIV suppression under cART, HCV coinfection was found to hamper CD8 þ downregulation. Further studies will determine the impact of treatment with direct-acting antiviral agents on the CD8 þ pool, and the advantage of systematic HCV-targeted therapy for HIV/HCV-coinfected patients.