Adenoid cystic carcinoma formerly called cylindroma is rare tracheal tumor. Characteristics of adenoid cystic carcinoma are infiltrative nature with local recurrence tendency and long natural course of the disease. Adenoid cystic carcinomas develop most commonly in the trachea. Primary resection and end-to-end anastomosis of the involved airway are treatment of choice. And postoperative radiation therapy might be useful, particularly when the surgical margins are not ample. We report two cases of adenoid cystic carcinoma of trachea diagnosed by flow-volume curve.