Because primary renal-cell carci�noma is relatively unresponsive to chemotherapy or radiotherapy, the resection or ablation of early-stage disease is the only option with a possibility of cure [1]. However, most small renal masses are now de�tected incidentally during ultra�sound, computed tomographic, or magnetic resonance imaging (MRI) examinations for nonuro-logic indications, in patients with no clinical signs of renal-cell carci�noma, such as persistent micro�scopic hematuria [2]. A substantial proportion of these smaller masses are benign (Table 1) [3].Ultrasound, computed tomo�graphic, and MRI techniques can definitively characterize some be�nign lesions, such as fat-containing angiomyolipomas and simple renal cysts. Otherwise, all non-fat-con�taining lesions that enhance after the administration of intravenous contrast agents are considered sus�pect for cancer [2,4]. Until re�cently, percutaneous biopsy was not considered accurate enough for diagnosis. Therefore, masses thatwere not definitively benign on im�aging were routinely resected or ab�lated without confirmed diagnoses of malignancy because of the high likelihood of renal-cell carcinoma. Recent advances in radiologic and pathologic techniques have in�creased the accuracy of image-guided percutaneous biopsy, and its use has been shown to decrease the likelihood of finding a benign lesion on nephrectomy [5]. There�fore, percutaneous biopsy plays a role in the diagnosis and manage�ment of small renal masses and can spare unnecessary and potentially morbid surgical procedures.