Bronchogenic cysts are common cystic lesions in the mediastinum. Most are located in the middle or posterior ares of the mediastinum, especially around the carina. We encountered a patient with a mass in the superior and anterior areas of the mediastinum, where bronchogenic cysts are not usually found. The mass was therefore, thought to be a thymic cyst. The cyst was located just behind the sternum and in front of the left brachio-cephalic vein, and was 5.5 x 3.5 x 1.2 cm. It originated in the upper and median part of the thymus, and was not attached to the respiratory tract. Histological examination showed ciliacted epithelium and a layer of smooth muscle in the wall of the cyst. The cyst contained viscid, yellowish, turbid fluid. Preoperative computed tomography and magnetic resonance imaging showed findings characteristic of bronchogenic cysts, except for the location. We know of no previous reported case of a thymic cyst resembling a bronchogenic cyst.