Plasma creatinine dosage is routinely used to estimate GFR but it is closely correlated to age, sex, weight and ethnic origin of the patients. All these factors make creatinine unreliable for GFR estimation. Laboratory dosage of creatinine may be performed with different techniques (JAFFE or enzymatic dosage) with a 20% variation in the results for the same patient. None of the GFR estimation formulae (Cockcroft et Gault or MDRD) have been validated in HIV patients. Cystatin C, a new marker still under evaluation, seems to show some interest in such patients because of its relative independency with regard to muscle mass, but has not been tested in HIV patients. Some cystatin C based formulae have been proposed but not yet tested and validated in HIV patients. HIV infected patients may exhibit abnormal body composition particularly affecting lipids but also, as shown recently, muscle mass. Our study will precisely measure body composition in order to allow interpretation of the variations of the renal markers with regard to muscle mass.