Twenty-one patients with carcinoma in situ of the larynx were treated with definitive irradiation from 1959 to 1987. The in situ changes were limited to 1 vocal cord in 19 patients, and to both vocal cords in 1 patient. One patient demonstrated extensive in situ changes involving the vocal cords bilaterally, as well as the anterior commissure, with both supraglottic and infraglottic extension. The mean follow-up from completion of treatment was 6.2 years, with a median of 50 months. Definitive irradiation resulted in a local control rate of 95%. The patient with extraglottic spread of in situ changes experienced a local failure 7 months after completion of treatment and, despite surgical salvage, died of local recurrence. This patient represents the only recurrence in our series. Our data suggest that radiation therapy can provide excellent control in carcinoma in situ limited to the true vocal cord.