This report describes the ultrastructural and hormonal characteristics of the recently described large-cell calcifying Sertoli cell tumor of the testis, a rare subtype of pure Sertoli cell tumor. The ultrastructural findings showed similarity to normal Sertoli cells, pure Sertoli cell tumors, Sertoli cells in azoospermic human testes, and the Sertoli cell component of Sertoli-Leydig cell tumors. Ultrastructure indicated features common to steroid-producing cells. Testosterone and estradiol were demonstrated in the tumor by immunocytochemical and biochemical methods.