We report three additional cases of primary extrarenal Wilms' tumor and review those cases previously documented. Analysis of the location, histopathology, treatment, and survival of these cases supports the following conclusions: Wilms' tumor may occur in an extrarenal location without primary renal involvement and must be included in the differential diagnosis of abdominal, pelvic, and inguinal masses; an extrarenal location supports a more frequent occurrence of ectopic metanephric blastema than was previously recognized or origin of Wilms' tumor from a more primitive mesodermal tissue; and the natural history and prognosis of extrarenal and renal Wilms' tumors appears similar.