OBJECTIVE To report the treatment outcomes of definitive radiotherapy (RT) for early-stage squamous cell carcinoma (SCCA) of the glottic larynx. METHODS We retrospectively reviewed the medical records of 585 patients with T1N0 to T2N0 invasive SCCA of the glottic larynx treated between 1964 and 2006 with RT alone. All patients had at least 2 years of follow-up, had histologic diagnosis of invasive SCCA, and received continuous-course RT. None of these patients received chemotherapy or had elective nodal RT. The probabilities of local control (LC), ultimate LC, ultimate LC with larynx preservation, neck control, cause-specific survival (CSS), and overall survival (OS) were calculated by the Kaplan-Meier product-limit method. RESULTS The median follow-up for survivors was 12 years. Five-year LC rates were as follows: T1A, 94%; T1B, 93%; T2A, 80%; and T2B, 70%. Multivariate analysis revealed that overall treatment time greater than 41 days (p = 0.001) and poorly differentiated histology (p = 0.016) adversely affected LC. Five-year rates of ultimate LC with laryngeal preservation were: T1A, 95%; T1B, 94%, T2A, 81%; and T2B, 74%. Twenty-four (4%) of 585 patients failed in the neck; only 7 neck failures (1%) were isolated. Five-year CSS and OS rates were as follows: T1A, 97% and 82%; T1B, 99% and 83%; T2A, 94% and 76%; and T2B, 90% and 78%, respectively. Ten (1.7%) patients had severe and/or fatal complications. One patient died of a radiation-induced carotid artery angiosarcoma. CONCLUSIONS Based on our study results, RT cures a high proportion of patients with T1N0 to T2N0 glottic SCCAs and has a low rate of severe complications.