One documented case of Wilms' tumor in an adult patient is presented. The patient is diagnosed clinically with renal tumor, probably renal carcinoma. Wilms' tumor is extremely difficult to diagnose preoperatively in an adult patient. The pathologic hallmarks of this neoplasm are distinctive and it is histologically similar to the childhood tumor. The therapeutic guidelines and surgical principles governing childhood Wilms' tumor should be applied to adult Wilms' tumor. This patient is still alive after 15 months.