We report the case of a 20-years old female patient with a tumor in the anterior mediastinum which was coincidently detected by a conventional X-ray of the chest. Differential diagnose were eliminated was constructed by means of computed tomography showing area of fatty density. The tumor was exstirpated because of its possible malignancy as well as the possibility of the development of local complications. Histology confirmed the tentative diagnosis of fatty cystic teratoma.