The incidence of developing malignancy in a mature cystic teratoma of the ovary is 1-2%. Most of the reported cases occur in postmenopausal women. This paper reports two cases of squamous cell carcinoma arising in a mature cystic teratoma of the ovary of which one occurred in a young woman. In the other case we could support the fact that the carcinomatous component has its origin in the columnar epithelium and epidermis of the teratomatous tissues.