mediastinal teratomas are encountered commonly in adult life, and rarely in childhood. Characteristically, these mediastinal teratomas are located anteriorly with only rare examples in the posterior mediastinum. The cystic teratoma usually behaves as a benign neoplasm, but the solid [non-cystic] teratoma is frequently malignant. We experienced a case of large anterior mediastinal cystic teratoma in a two-years old boy, which was treated by complete surgical excision with good result.