Surgical treatment of multiple or recurrent renal tumors may be complicated by renal function impairment. Mini-invasive thermotherapy as radiofrequency (RF), induces necrosis of tumoral tissue while sparing normal renal parenchyma. The purpose of the study is to compare, in patients at risk of renal insufficiency, a strategy based on surgical approach and a strategy based on RF approach. 180 patients from 9 centers will be randomized in two groups (surgical vs. RF, delivered either percutaneously or under laparoscopy). The proportion of patients with a local carcinologic efficacy at 5 years and the general and renal tolerance will be analysed and compared between both strategies.