Benign cystic teratoma of the ovary (BCTO) is the most common ovarian germ cell tumor occurring predominantly in early adulthood. Malignant transformation of a BCTO is rare, with an incidence of 2%. Most benign cystic teratomas with malignant transformations are squamous cell carcinomas with just 6.8% being adenocarcinomas. We present a rare case of adenocarcinoma arising from the gastrointestinal epithelial elements of BCTO based on the microscopic examination and immunohistochemical studies. Adenocarcinoma arising from gastrointestinal epithelium within BCTOs is extremely rare. This is the fifth reported case of adenocarcinoma arising in gastrointestinal epithelium of a BCTO.