Uterine tumors with histologic resemblances to ovarian sex-cord tumors were encountered in 14 women in the fourth to sixth decades of life, most of whom had abnormal vaginal bleeding and enlarged uteri suggesting leiomyomas. The tumors in six cases (Group I) were identical to one or another form of well-recognized endometrial stromal tumor except for focal epithelial-like differentiation resembling that seen in sex-cord tumors. These tumors were mostly poorly circumscribed large mural masses. The focal sex-cord-like differentiation was manifested by cords, trabeculae, nests and tubules of epithelial-like cells; eosinophilic bodies resembling Call-Exner bodies were seen in one case. Five of the six patients with tumors of this type have been followed for postoperative intervals of 22 months to 15 years, and pelvic recurrences have developed in three. The tumors in eight cases (Group II) differed from those in Group I by having a predominant or exclusive pattern reminiscent of an ovarian sex-cord tumor. These tumors, most of which were single, well-circumscribed, yellow to tan, mural masses 4 to 10 cm in diameter, appeared benign, with no recurrence during postoperative periods of four months to seven years. The relations of the two groups of tumors to one another and to previously described similar tumors. including so-called granulosa-cell tumors and "plexiform tumors" of the uterus, are discussed, and an origin from endometrial stromal cells is postulated.