The fetal rhabdomyomatous nephroblastoma is considered to be a predominantly monophasic mesenchymal variant of Wilms' tumor, which has not been seen in patients older than four years. It acts less aggressively than a Wilms tumor despite its much larger size. Its better prognosis appears to be related to either the absence of or the insignificant amounts of neoplastic epithelium. The bilaterality of this tumor in one-third of the cases, however, may negatively affect the overall prognosis, because complete resection may be impossible or because renal failure ensues.