Immature teratoma is a rare ovarian germ cell tumor with an aggressive clinical behavior. Treatment involves surgical resection, usually followed by chemotherapy. Since the introduction of postoperative chemotherapy several cases of "transformation" of this malignant tumor into mature teratoma (retroconversion) have been described. Usually retroconversion presents during the first year of diagnosis. We report a case of synchronous mature teratomas of the ovary and liver presenting 11 years following chemotherapy for stage III immature ovarian teratoma. The CT scan appearance, incidence, and biological significance of this phenomena are discussed.