Oncocytoma is a term generally used to describe a neoplasm of the renal parenchyma consisting of well-differentiated cells with prominently eosinophilic granular cytoplasm. We report our experience with such tumors and with 4 cases of granular cell carcinoma (grade 2). We present the histopathology, surgical staging studies, treatment, and clinical outcome. Of the 10 patients, 7 are alive without evidence of tumor at a mean follow-up of 5 years from the initial treatment. Three patients have died, 2 from nontumor-related causes while the cause of death of the third patient is uncertain, possibly due to the tumor. Although well-differentiated oncocytic renal tumors are usually considered as uncommon when the diagnosis is made, nonaggressive behavior is expected. However, careful radiographic and pathologic examination is required to avoid the pitfall of overlooking a higher-grade, more lethal neoplasm which may be mixed with the well-differentiated oncocytic neoplasm and form a minority component. A wide resection, which in most cases is nephrectomy, is apparently curative and assures that complete pathological examination of the specimen can be accomplished. In more than 90% of the cases, the tumor is solitary and unilateral. Cases in which there are multiple tumors are often bilateral, and this finding may create diagnostic confusion.