Kidney tumors in children are almost always embryonal nephroblastomas, commonly known as Wilms' tumors. These are only second in frequency to neuroblastomas among malignant neoplasms in children. The occurrence of renal-cell adenocarcinoma, usually termed hypernephroma, is most unusual in children. In 1938 Ladd1stated that he had not seen a single example of hypernephroma in 20 years at the Children's Hospital. He also commented that from a study of the literature the occurrence of true hypernephroma in childhood appears to be very rare. Bell2stated that about 95% of renal adenocarcinomas develop in persons over 40 years of age and doubted very much their existence in childhood. Melicow3could not find a single instance of renal adenocarcinoma in children among his review of 199 cases of renal tumors. Campbell4could only find four such tumors in the files of The American Tumor Registry. Cathcart5reported