Today, one of the challenges of HIV treatment is to overcome side effects and toxicity of long term antiretroviral therapy. A promising approach may be the simplification of treatment maintenance strategies, sparing certain antiretroviral drug classes. This is a two-year prospective phase II/III, multicenter randomized trial to evaluate the efficacy and tolerance of a lopinavir/ritonavir monotherapy as a maintenance regimen in HIV-infected adults. Enrolled patients must have had stable antiretroviral treatment and HIV-1 RNA below 50 cp/mL over the previous 12 months, and no prior treatment failure. Provided informed consent, 420 patients are randomized in a 1:1 ratio to two open-label treatment groups and receive either lopinavir/r 800/200mg per day or EFV/FTC/TDF 600/200/245 mg per day (fixed dose combination). The main objective is to assess treatment efficacy and tolerance after 2 years. In 80 patients, repeated DEXA measurements are performed during the trial in order to evaluate changes in bone mineral density and in body composition.