: Teratomas are classified as congenital germ-cell tumors. These tumors are composed of ectopic tissue from 2or 3 layers,including mature , immature or malignant components and usually occur along the midline of the body. These tumors commonly occur in ovaries,testes, retroperitoneum and the sacro-coccygeal region.Anterior mediastinal teratomas account for 8-13% of the tumors in this region. the majority of these teratomas are located in the anterior mediastinum with only 3-8% arising from

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... rior mediastinum. Cases Report: The first case:A 65 years old man referred with complain of chest pain and dysphagia. A very large benign cystic tumor in posterior mediastinum in patient's CT scan was detected and the patient underwent surgical resection. The final diagnosis was reported cystic teratoma . patient's symptoms were disappeared with surgical resection . The second case:A 55 years old woman with benign teratoma in anterior mediastinum tumor was discovered with assessment after chest trauma and she was treated with surgical resection.A30 month follow up was done, none of the patients had any complain. Conclusion: These slow growing tumors are often asymptomatic and are often detected incidentally on chest radiographs and or because of complications such as atelectasis,adhesion or compression of adjacent structures rupture and secondary infection. Surgical intervention is the only curative treatment and is advisable even when patient is asymptomatic because of the potential of complications.