A case of cystic partially differentiated nephroblastoma with immunohistochemical and serological demonstration of alpha-fetoprotein (AFP) production is described. To our knowledge, this is the first such case reported. The morphological heterogeneity of this rare tumor led us to describe the criteria of its nosological classification and of its differential diagnosis with intrarenal teratoma. AFP, besides being a marker of germline-derived tumor, was associated to this rare variant of Wilm's tumor. Although the tumor did not show regression either on clinical or pathologic assessments, serum AFP levels decreased after preoperative chemotherapy and returned to normal limits after nephrectomy.