The tumors of the kidney are around the 3% of the neoplasia in adult patients and, at the postmortem examination, the renal neoplasias has a frequency of 1/300 for tumors diameter of 1 to 2 cms. In the treatment of the small neoplasias, techniques of nephron sparing and enucleation are used. These techniques have shown the same therapeutic effectiveness of the radical nephrectomy in patients with tumors smaller than 4 centimeters, with reduction of morbidity. However, there are few clinical situation in which the surgery has a high risk: patients with solitary kidney, chronic renal failure, multiple localizations involving also contralateral kidney, in patients with other malignancies and in von Hippel-Lindau Syndrome. Recently, percutaneous mininvasive techniques have been applied (ex. thermoablation): these techniques allow to reduce the duration of general anesthesia, they offer the possibility to use spinal anaesthesia (besides deep sedation and general anaesthesia) with reduction in mortality during surgery. The most commonly used among interstitial therapies is the radiofrequency (RF), which changes electromagnetic waves into heat. RF used both tomography and ultrasound-guided. The latter is the most recommended because it allows to follow the procedure in real-time. The treatment of renal tumors with RF, in which surgery is inadvisable, is safe and effective especially in peripheral and/or exophytic lesions lower than 4 cm. However the larger tumors can also be treated successfully with combined therapy or multiple sessions.