Carcinosarcoma is a rare neoplasm which, in the female genital tract, arises mainly in the endometrium. Although the pathogenesis remains obscure, there is an apparent association between pelvic irradiation and uterine sarcomas. There have been sporadic case reports of the development of carcinosarcomas of the cervix, vagina, and extragenital areas, but not of the ovary, after previous pelvic irradiation. We describe a case of ovarian carcinosarcoma arising in a 74-year-old female who had pelvic irradiation 33 years previously. Exploratory laparotomy showed a 25 x 18 x 9 cm left ovarian tumor with adjacent organ invasion including peri-uterine serosa and rectum. The patient was treated by optimal cytoreduction, followed by chemotherapy with adriamycin and cisplatin. However, acute hepatitis caused by reactivation of hepatitis B virus infection developed just before the fifth course of chemotherapy. She died of hepatic failure two weeks later.