[Renal clear cell tumors: morphology, histochemistry, ultrastructure, differential diagnosis]

To define criteria for differential diagnosis of renal clear cell adenoma and grade I clear cell carcinoma, morphological, morphometric, histochemical, and ultrastructural studies were undertaken to examine 30 renal clear cell tumors (18 carcinomas and 12 adenomas). No morphological, morphometric, histochemical, and ultrastructural differences were found between the tumors, but the average tumor size was smaller in the adenoma than in the carcinoma. Clinically and morphologically, clear cell adenoma should be classified as grade I clear cell carcinoma of stage I, which has a relatively favourable prognosis by virtue of its small node sizes.