From January 1984 through December 1987, 41 patients with squamous cell carcinomas of the supraglottic larynx were treated with hyperfractionated radiotherapy at The University of Texas M. D. Anderson Cancer Center. Two patients had T1 primary tumors, 23 had T2, 15 had T3, and 1 had T4; 29 patients had no clinical evidence of nodal disease in the neck, 4 had N1, 5 had N2, and 3 had N3. Radiotherapy was delivered in 120 cGy fractions twice per day, with at least 4 hr between treatments. Total doses ranged from 7200 to 7900 cGy (median, 7680 cGy). Three patients had planned neck dissections before or after radiotherapy, and three patients with fixed vocal cord lesions were treated with preradiation chemotherapy. At the time of analysis, median follow-up was 22 months. Four patients have had failures at the primary tumor site. There has been one recurrence in the neck in a patient who also had a recurrence at the primary site. Three of the four patients with recurrences have been successfully treated with salvage surgery. Exclusive of surgical salvage, the actuarial disease-free local control rates above the clavicles in the 38 patients with T2 and T3 cancers were 96% at 1 year and 87% at 2 years. In comparison, the rates were 82% and 76% for a group of 98 patients with T2 and T3 lesions treated at this institution from 1970 to 1981 with 6500-7000 cGy given in 200 cGy fraction per day. As predicted, acute reactions were more severe but late complications were not increased in patients who received hyperfractionated radiotherapy compared with those treated by conventionally fractionated therapy. Only two patients have developed severe late complications one of whom required laryngectomy. Hyperfractionated radiotherapy appears to provide improved local control with a similar incidence of late complications when compared with conventionally fractionated therapy. To further improve the therapeutic ratio, our current protocol has been amended by reducing the large field dose per fraction to 110 cGy (with a 2 day protraction of overall time) and requiring a minimum interfraction interval of 6 hr.