OBJECTIVE To evaluate the effect of host, tumor, and treatment-related variables on local control and survival in patients with T1N0M0 squamous cell carcinoma of the glottis. METHODS Ninety-one patients with T1N0M0 squamous cell carcinoma of the glottic larynx were analyzed. Median follow-up was 9 years (range 2-25). Patients were treated with daily fractions of 180 cGy to 220 cGy to doses of 5925-7000 cGy (median 6400). The following factors were analyzed: age, sex, histologic grade, disease extent, beam energy, field size, total dose, dose per fraction, and elapsed treatment days. RESULTS The 5-year actuarial local control was 80%. On univariate analysis, only elapsed treatment days and dose per fraction were significant factors for local control. Local control was 100% if treatment was completed within 42 days, 91% for 43-46 days, 74% for 47-50 days, 65% for 51-54 days, and 50% for 55-66 days (p = 0.0001). In patients treated at < 200 cGy per fraction, local control was 62% as compared to 87% for > or = 200 cGy per fraction (p = 0.006). On multivariate analysis, only elapsed treatment days was a significant factor for local control (p = 0.0001). The 5-year actuarial survival for the whole group was 92%. Elapsed treatment days was the only variable affecting survival. Survival was 100% if treatment was delivered within 42 days, 96% for 43-46 days, 94% for 47-50 days, 91% for 51-54 days, and 67% for 55-66 days (p = 0.02). The 5-year actuarial disease-specific survival was 95%, with treatment duration again being the only significant prognostic factor. Disease-specific survival was 97% for treatment completed within 39-54 days versus 80% for 55-66 days (p = 0.02). Only three (3.3%) patients experienced moderate or severe complications. None of the evaluated parameters impacted significantly on complications. CONCLUSIONS We conclude that elapsed days is the most prognostically significant factor for local control and survival in patients treated with radiotherapy for T1 squamous cell carcinoma of the glottis. We recommend that these patients be treated with 210 cGy daily fractions to 6300 cGy.