Teratomas are rarely seen in adults, and presacral region is an area where they rarely settle in. Similarly, only about 1% of teratomas show malignant transformation. Malignant transformation is often associated with the area where teratoma settles in. Malignant transformation of mediastinal teratomas is more frequent than the ones located in retroperitoneal area and gonad. They most commonly show rhabdomyosarcoma, primitive neuroectodermal tumor, enteric adenocarcinoma, and leukemia transformation. In teratomas showing malignant transformation, the clinical course is aggressive; and survival of patients with metastatic disease is very low. The primary treatment of teratomas with malignant transformations is surgical. Effect of radiotherapy and chemotherapy is not clear in patients, to whom surgical operation cannot be applied, or those who are with residual tumor, even if surgical operation can be applied to them, or those who are at metastatic stage. In this paper, we presented a 76-year-old male patient due to the histologic diagnosis of mucinous adenocarcinoma within teratoma, in whom approximately 7 cm presacral mass was found during the radiographic examination made by the reason of low back pain and pelvic pain.