The investigators report a case of a 39-year-old man who presented an anterior mediastinal cystic mature teratoma. Those kind of tumor contain elements derived from more than one of the three primary germ layers (ectoderm, mesoderm, endoderm), frequently arranged in a haphazard manner. They arise from totipotent cells and, therefore, are primarily found in gonads, and more rarely in primitive cells kidnapped in other parts of the body. The tissues are immature to well differentiated and foreign to the anatomic site. Mature teratomas are either cystic or solid, although the cystic presentation predominates in gonadal sites. Benign teratomas are the most common mediastinal germ cell tumor, accounting 70% of the mediastinal germ cell tumors in children and 60% of those in adults. Immature teratomas are potentially malignant tumors; their prognosis is influenced by the anatomic site of the tumor, patient age, and the fraction of the tumor that is immature. Treatment of benign mediastinal teratoma includes complete surgical resection, with results in a excellent long-term cure rates. Complete resection of teratomas should be the goal of treatment.