The study has been designed to test the hypothesis that in patients co-infected with HIV and HCV who exhibit maximal virologic suppression on a double class antiretroviral (ARV) regimen, including two Nucleoside Reverse Transcriptase Inhibitors (NRTIs) and a Non-nucleoside Reverse Transcriptase Inhibitors (NNRTI) or a Protease Inhibitor (PI) (boosted or not with ritonavir), simplification of highly active antiretroviral therapy (HAART) to Kaletra® monotherapy will represent a viable strategy without any negative impact on the virologic control of HIV infection.