To our knowledge, diffuse involvement of renal parenchyma by multiple minute foci of clear cell proliferations has not been previously reported. We report such a case, found incidentally, in an 86-year-old woman who had undergone right ureteronephrectomy for pyeloureteral urothelial carcinoma. Macroscopy of the kidney showed numerous yellow dot-like cortical nodules less than 0.3 cm. Histologic examination of the kidney and nodules revealed innumerable foci of minute clear cell proliferations in a background of chronic pyelonephritis. The benign or malignant nature of those clear cell microtumors was investigated by immunohistochemistry and fluorescent in situ hybridization analysis of chromosome 3p.