A 45-year-old male was admitted to Nagoya University Hospital with dyspnea. He was examined by chest X-ray, CT, MRI, and bronchofiberscope. The chest X-ray showed a large abnormal shadow in the right lung field. A large tumor mass pressing the right lung occupied a half of thoracic cavity on a chest CT and MRI. Bronchofiberscopic findings showed a stenosis of the right intermediate bronchus. The clinical diagnosis was posterior mediastinal tumor. He underwent a posterolateral thoracotomy and the tumor was removed smoothly. The size of resected specimen was 15 x 13 x 11 cm. Histopathological examination of the specimen revealed a mediastinal neurilemmoma. He has been well for 4 months postoperatively.