A rare case of simultaneous occurrence of Wilms' tumor in the left kidney and the bladder.

Wilms' tumor is the most common malignant solid tumor of the kidneys in children. Extrarenal Wilms' tumor is extremely rare. Herein, we report an 8-month-old boy with a chief complaint of frequent micturition and dysuria for 10 days. Physical examination and ultrasonography evaluation revealed simultaneous involvement of neoplasms in the left kidney and the bladder. Following excision of the masses, both were identified as Wilms' tumor by histopathology and immunohistochemistry. The two neoplasms are presumed to have developed independently because of the different pathological manifestation.