[Undifferentiated renal sarcoma or Wilm's tumor (author's transl)]

About a case in a six year old Negro boy, the existence of a special pattern among the malignant renal tumors in children is emphasized; this tumor is marked from the Wilms' tumor by its peculiar behaviour (frequently poor evolution, high incidence of osseous metastasis in contrast with the rate occurrence of pulmonary involvement) and by a sarcomatous appearance at the pathologic examination. The classification and the suitable therapeutic management are discussed.