We report our recent findings on the diagnosis, incidence, appearance of the trachea at autopsy, and surgical treatment of acquired trachobronchomalacia. In the diagnosis of this disease, continuous dynamic CT scanning (1 slice/0.6 second) from inspiration to deep expiration was better than X-ray cine recording. It is difficult to observe the most collapsed airway on coughing using bronchofiberscopic recording, because its duration time was estimated to be 1/10 second by X-ray cine recording, whereas the findings at one instant were easily recorded by video-bronchoscopy on coughing. The degree of severity of this disease was classified into three groups. 1st degree 0-50% narrowing of airway caliber, 2nd degree 50-75%; and 3rd degree 75-100%. Severity of 2nd or 3rd degree was present in 542 (12.7%) of 4283 patients suffering from chest disease who underwent bronchoscopy. Seventy-two percent of patients were aged 50 to 80 years. Third degree tracheomalacia was found in 131 patients with an incidence of 3.1%, which increased from 2.2% at 50 years to 6.2% at 80 years. The autopsy findings of the trachea consisted of fragmentation of the tracheal cartilage and extension of the membranous portion. The pathogenesis may be varied with different types of collapse of the airway, including the saber sheath type and the crescent type. Surgical treatment consists of prevention of the airway collapse by wrapping the airway with Marlex mesh and bonding Lyodura (lyophilized dura mata) with fibrin glue, which is more reliable than the span plasty proposed by Nissen.