To clarify the role of postoperative radiotherapy for adenoid cystic carcinoma of the tracheobronchial system (ACC), we analyzed patients treated at the National Cancer Center Hospital, Tokyo. Seven patients with ACC were treated with resective surgery and postoperative radiotherapy from 1962-1990. None of the primary lesions was completely surgically resected. Postoperative irradiation was delivered by standard fractionation at a dose range of 49.2-72 Gy. Four of seven patients lived more than 5 years, up to 21 years, without local recurrence. In contrast, three other patients who showed recurrence within 2 years died of disease before 5 years. Three of four patients who received postoperative irradiation of 60 Gy or more attained local control. One of three patients who received less than 60 Gy failed locally. A high dose of postoperative radiotherapy for patients with a positive surgical margin of ACC seems to improve local control and result in long-term survival.