Report on a case of sclerosing stromal tumor of the ovary with detailed pre- and postoperative hormonal analysis and an electron microscopic study of the tumors. The tumor was secreting both estrogenic and androgenic hormones. Ultrastructural studies have corroborated previous light microscopic findings on the variegated appearance of the tumor and the abundance of collagen among the cells and indicated that the tumor is functionally active and of ovarian stromal origin.