Saber-sheath trachea constitutes a morphologic-functional disorder of the intrathoracic segment, characterized by an abnormal configuration of the tracheal cartilages, where the coronal diameter represents less than 2/3 of the sagittal, with narrowing of the front bow and collapse of the side wall during coughing and stressed expiration. Just as it happens in the case of semilunar configuration of the thacheal expiratory collapse syndrome, it is more common in patients with COPD, when the clinicradiologic appearance usually masks the seriousness of the functional disorder. The authors demonstrate the clinic-tomographic-endoscopic-functional correlation in the case of a 43-year-old female patient suffering from severe chronic obstructive respiratory failure whose clinic-radiologic condition masked the seriousness of the dysfunction, emphasizing the need for systematic investigation of the tracheal dynamics in this type of case.