PURPOSE: The end results after radiation therapy for T1-T2N0 glottic carcinoma vary considerably. We analyze patient-related and treatment-related parameters that may influence the likelihood of cure. PATIENTS AND METHODS: Five hundred nineteen patients were treated with radiation therapy and had follow-up for >or= 2 years. Three patients who were disease-free were lost to follow-up at 7 months, 21 months, and 10.5 years. No other patients were lost to follow-up. RESULTS: Local control rates at 5 years after radiation therapy were as follows: T1A, 94%; T1B, 93%; T2A, 80%; and T2B, 72%. Multivariate analysis of local control revealed that the following parameters significantly influenced this end point: overall treatment time (P < .0001), T stage (P = .0003), and histologic differentiation (P = .013). Patients with poorly differentiated cancers fared less well than those with better differentiated lesions. Rates of local control with laryngeal preservation at 5 years were as follows: T1A and T1B, 95%; T2A, 82%; and T2B, 76%. Cause-specific survival rates at 5 years were as follows: T1A and T1B, 98%; T2A, 95%; and T2B, 90%. One patient with a T1N0 cancer and three patients with T2N0 lesions experienced severe late radiation complications. CONCLUSION: Radiation therapy cures a high percentage of patients with T1-T2N0 glottic carcinomas and has a low rate of severe complications. The major treatment-related parameter that influences the likelihood of cure is overall treatment time.