Renal oncocytoma is one of the most unusual benign lesions, which presents as a complicated mass resulting in a diagnostic and therapeutic dilemma. A new case of renal oncocytoma in a 13-year-old boy is presented. The clinocopathologic features of this rare entity are discussed, with special emphasis on diagnosis and treatment. There are no specific presumptive clinical and laboratory findings, including tumor markers, ploidy analysis, and imaging techniques that distinguish oncocytoma from other renal masses. The most important diagnostic aid is to bear this entity in mind when a child presents with an unexplained renal mass. Frozen section biopsies followed by partial nephrectomy are mandatory for the appropriate treatment after excluding bilateral or multifocal occurrence. J Pediatr Surg 35:1396-1398. Copyright (C) 2000 by W.B. Saunders Company.