Background: Mediastinal mature teratoma is a rare primary germ cell neoplasm composed of welldifferentiated tissues derived from more than one of the three embryonic germ cell layers. Almost all mediastinal teratomas are found in the anterior mediastinum. Only eighteen posterior mediastinal teratomas
have been reported to date in the literature. They have an excellent prognosis if tumor resection is complete and no immature tissue is present in the tumor.
Case report: We describe a case of a two month-old baby boy who developed a mature cystic teratoma in the posterior mediastinum, successfully treated by surgical excision. The incidence, etiology and diagnostic
procedure of the posterior mediastinal teratoma is discussed.
Conclusions: Mature cystic teratomas of the posterior mediastinum are distinct clinical entity that must be considered when caring for a patient with a posterior mediastinal mass. Because of surrounding vital structures
the cyst should be treated without delay.

Keywords: Teratoma, posterior mediastinum, Mediastinal Neoplasms