 The use of tacrolimus in the long term as part of the immunosuppressive regimen after transplantation is associated to complications such as chronic nephrotoxicity, impaired glucose metabolism diabetes mellitus and an increase of the incidence of neoplasia. The conversion from a tacrolimus based therapy to a sirolimus based therapy associated with mycophenolate mofetil could improve the incidence of such complications. The aim of this study is to assess the riskbenefit ratio of this switch performed in stable renal transplant recipient between 12 months and 36 months after transplantation. The incidence of a composite endpoint worsening of GFR evaluated by MDRD formula, incidence of cancer and diabetes will be assessed 24 months after conversion. 