Mature cystic teratoma (MCT) is the commonest germ cell neoplasm of the ovary but malignant transformation is a rare occurrence (1-2%). Of these malignancies documented in literature the commonest are squamous cell carcinoma and adenocarcinoma. Urothelial carcinomas arising in an MCT are a rare occurrence and only 7 cases have been reported in literature. We report a case of an MCT which was complicated by the presence of urothelial carcinoma confirmed on histopathological examination.