A 51-year-old woman had localized interstitial pneumonia that rapidly progressed to involve all lung fields. After 9 days of conventional mechanical ventilation, pneumothorax developed in the presence of an obstruction of the right main bronchus. Bronchoscopy and endobronchial biopsies revealed NTB involving the tracheobronchial tree distal to the tip of the endotracheal tube, with complete obstruction of the right main bronchus by hard, eschar-like material. Tracheal mucosa proximal to the tip of the endotracheal tube was normal. Subsequent bronchoscopy, 20 days later, showed marked resolution of NTB. Though a frequent complication of mechanical ventilation in the neonate, NTB as a complication of conventional mechanical ventilation has not previously been recognized in an adult. Necrotizing tracheobronchitis should be suspected in adults who have had mechanical ventilation and who are experiencing ventilatory difficulties, after routine problems have been treated or excluded.