Teratomas, usually arising in the anerior mediastinum, are very uncommon in the posterior mediastinum. Embryologic development of anterior mediastinal teratoma is thought to be from thymic anlage which descends fromthe third branchial cleft and pouch, while that of posterior mediastinal teratoma is thought to be from theremnant of notochord. CT findings of posterior mediastinal teratomas are not different from teratomas elsewhere,containing fat, calcification, soft tissue and thick walled cyst. Ultrasonographic findings are mixed echogenicmass containing cystic portion, highly reflective solid portion and area of acoustic shadowing. Authors recentlyexperienced 2 cases of surgically proven posterior mediastinal teratoma and report with review of literature.