The question arises as to whether there are 2 entities that coexist or that represent a single neoplasm. Renal cysts in children and infants are rare and represent developmental aberrations in the mesonephric blastema. This renal lesion may represent the coincidental association of a nephroblastoma and a multilocular cyst of the kidney. The diffuse distribution of the nephroblastomatous tissue between the cysts suggests that the cysts are an integral part of the tumor, and the cysts represent dilated tubules. Nephroblastomas exhibit a broad range of differentiation when classified according to the extent of differentiation toward mature renal tissue. Most nephroblastomas fall into an intermediate category, the differentiated and undifferentiated tumors being less common. The polycystic nephroblastoma should be considered a well differentiated tumor and may be benign. This implies that this tumor has a good prognosis and is amenable to surgical removal.