A case of testicular specialized gonadal stroma tumor was evaluated by histologic, ultrastructural and immunohistochemical techniques in a young adult male patient. The neoplastic cells were organized in cords or tubular structures delimited by a basement membrane. The ultrastructural findings suggested a diagnosis of a partially differentiated Sertoli cell tumor. This was also supported by the presence of a vimentin rich cytoskeleton, which is normally present in Sertoli and Leydig cells. The tumor cells did not secrete steroid hormones, as suggested by clinical findings, as well as by hormonal, immunohistochemical, and ultrastructural observations.