A testicular granulosa cell tumor of the adult type was studied in a 61-year-old man with a history of diabetes and urinary bladder carcinoma. The tumor was composed of three areas, each with a distinctive histologic pattern: solid, cystic, and cordlike. Most of the tumor cells in the three patterns had a round to ovoid euchromatic nucleus with one or two large nucleoli and scanty cytoplasmic organelles, mainly mitochondria and rough endoplasmic reticulum. These cells showed slight immunopositivity for vimentin and no immunostaining for cytokeratins. Occasionally, elongated nuclei displaying membrane infoldings were observed. Pleomorphic nuclei were rare. The number of mitotic figures was low. Differential aspects of testicular and ovarian granulosa cell tumors are discussed.