We report a case of sub-glottis stenosis encountered during anesthetic induction. A 79 year-old male was scheduled for a right partial lung lobectomy with video assisted thoracic surgery. Significant history includes percutaneous coronary intervention and pacemaker insertion for myocardial infarction, tuberculosis, trache- ostomy and radiation therapy for vocal cord cancer. Difficulty in tracheal intubation was predicted, but chest X-ray and CT scan did not show tracheal steno- sis. General anesthesia was induced smoothly and mask ventilation was easy. The vocal cord was fully exposed by McGRATH® MAC laryngoscope. However, inser- tion of double lumen tube (37 Fr) was impossible because of resistance just under the vocal cords. A membranous subglottic stenosis was found using a flexible bronchoscope. Then we inserted ID 7.0 mm single lumen tube and accomplished differential lung ventilation using a bronchial blocker. Surgery was done smoothly. In spite of recent advances in radiographic imaging, some cases of tracheal stenosis are difficult to diagnose.