Although foci of calcification in renal cell carcinoma is frequently observed, ossification is extremely rare and may be a marker for favorable prognosis. We report a case of renal cell carcinoma with a focus of ossification; this case was not detected with imaging techniques prior to surgery and diagnosed initially on pathologic examination, unlike other cases. If the radiographic evaluation for ossification is inconclusive but the mass is extremely hard to palpate or difficult to cut, the surgeon should remember the favorable prognosis of such lesions and might consider a limited procedure such as partial nephrectomy while waiting for pathological analysis.