médiastinal Coelomic cysts are rare cysts of mesothelial origin. They represent 4 to 11% of all mediastinal tumors. It affects both men and women. The diagnosis is often made in adulthood. They are often asymptomatic We repport the rare case of mesothelial cyst of mediastinum. A 38-year-old woman with no medical history, she was reffered to our department after chest X-ray showed a giant anterior madiastinum. The lesion was resected by VATS, which revealed a médiastinal cystic that extends from the top of the anterior mediastinum to the diaphragm. On histological section, the cystic wall is seat of a significant inflammatory, lined by a flattened epithelial lining of mesothelial type, conclusive to mediastinal pleural mesothelial cyst. The prognosis is excellent in the short and long term.