The authors report four cases of renal oncocytoma investigated by echography and proved by histology after surgery. Describing the clinical cases, after a brief review of the literature, the radiologic findings are analysed with particular regard to the sonographic signs that can preoperatively differentiate oncocytomas from carcinomas. The authors conclude that the only sonographic distinguishing feature is a quite characteristic central hyperechoic streak corresponding to the fibrous scar, frequently found in this benign tumor.