Tracheobronchial adenoid cystic carcinomas are rare tumors that progress slowly. Diagnosis by chest plain radiography is difficult, and suspecting the existence of a disease that causes stenosis in the airways is an important key for diagnosis. A 51-year-old woman referred to our hospital because of dyspnea on exertion. Chest plain radiograph showed a slight widening of the mediastinum. The flow–volume curve of respiratory function test revealed flat portions of the curve suggesting the central airway obstruction pattern. Chest CT confirmed the existence of tracheobronchial tumor, which was pathologically diagnosed as adenoid cystic carcinoma. Chest physicians and thoracic surgeons should be careful not to miss these trivial findings in the first inspections
