A case of a cystic partially differentiated nephroblastoma treated with combined chemotherapy after removal in a 2-month old newborn is reported. Cystic partially differentiated nephroblastoma is a newly described clinicopathologic entity, involving elements of a nephroblastoma and cystic disease, and it is believed to be a pathologic derivative of the metanephric blastema and not related to renal dysplasia. Cystic partially differentiated nephroblastoma is distinguished from multilocular cysts of the kidney by the presence of partially differentiated renal elements in the septa of cysts. The aggressive appearance of the cells led to the treatment of this tumor as potentially malignant.