Squamous cell carcinoma arising from ovarian mature cystic teratoma (MCT) is very rare. We report a case of a 21-year-old female who presented with a 7-month history of abdominal mass increasing in size with time. Imaging findings were suggestive of bilateral ovarian teratoma. Intraoperative findings were cystic masses in both ovaries and a solid multinodular left mesenteric mass. On gross examination, there were cysts filled with gelatinous material and hairs, while the mesenteric mass consisted of matted lymph nodes. Histology revealed a MCT with multifocal areas of invasive squamous cell carcinoma, in all three masses. While squamous cell carcinoma in MCT is very rare, this is a unique case reported in a so young patient. The younger age could not be a factor preluding malignancy in MCT.