Nephroblastomas are usually solitary, large, and sharply demarcated tumors. The bulging cut surface is soft, fleshy, lobulated, yellow-tan, and frequently has areas of hemorrhage or necrosis. About 7% are multicentric and 5% of cases are bilateral. Wilms tumor is the 4th most common pediatric malignancy in the US and affects 1 in 10,000 children in the US. The peak incidence is seen between 2 and 5 yrs. It is only rarely seen as a congenital neoplasm - an important distinguishing feature from mesoblastic nephroma.