The prognosis and natural history of the teratoma depends on the presence or absence of immature tissue and the age of the patient. Approximately 80% of teratomas are mature. Immature teratomas appear in infancy and childhood and are often treated successfully with surgical excision, although they can, in rare instances, recur and metastasize.13 Immature teratomas in adults often have an aggressive course and a poor prognosis. Less commonly, a mature teratoma can develop a focus of carcinoma, sarcoma, or malignant germ cell tumor, and is then referred to as a “malignant teratoma” or “teratocarcinoma.”13 Teratocarcinomas can result in death within a few months of diagnosis as a result of local spread or distant metastasis, and therefore surgical excision of all suspected teratomas is recommended. Chemotherapy may be associated with improved survival in some cases of metastatic teratocarcinoma.56,57 In contrast, in resected mature teratomas, recurrences have not been described. Histologic examination of the resected mass is essential to determine whether a small focus of immature tissue or remnants of another germ cell tumor, carcinoma, or sarcoma are present. Notably, dense adhesions may be present at the time of surgery due to the leakage of fat into the mediastinum or the presence of functioning endodermal pancreatic tissue. With extensive teratobronchial communication, lobectomy or even pneumonectomy may be required.