Mature cystic teratoma is a benign neoplasm, but malignant transformation of one component may occur in 2% of cases. Although very different types of carcinomas may be arise from mature cystic teratoma, invasive squamous cell carcinoma is the most frequent type of malignancy found, comprising about 80% of all malignancies arising from dermoid tumours. Although invasive squamous cell carcinoma is relatively frequent, it is surprising that so few cases of squamous cell carcinoma in situ in mature cystic teratoma have been reported. We describe a case of squamous cell carcinoma in mature cystic teratoma without an invasive component.