The malignant Brenner tumor is an unusually rare lesion, and thus far only six cases have been reported in the literature. Forty-two cases of Brenner tumor were reported from the Mayo Clinic in 1950, all of which were benign.1 However, a malignant Brenner tumor was seen in 1954. A report of this case is presented herewith. Report of Case A 59-year-old white woman (sextigravida, quadripara, two abortions) was first seen at the Clinic in 1938 because of symptoms referable to a duodenal ulcer. Pelvic examination at this time revealed a leiomyoma in the uterus 3 to 4 cm. in diameter. In 1954 the patient returned, complaining of lower abdominal enlargement of two weeks' duration. She reported that the menopause had occurred in 1947. On examination a firm, somewhat nodular mass was found in the left adnexal region. Abdominal hysterectomy and bilateral salpingo-oophorectomy were carried out. The uterus was not