The number of patients aged > or =75 years who present with a stage I nonsmall cell lung cancer (NSCLC) is increasing. Elderly patients often have significant comorbidity and may be unfit for surgery. Furthermore, surgery in the elderly is associated with increased mortality and morbidity. In this study, the authors evaluated the outcomes of stereotactic radiotherapy (SRT) in elderly patients. Since 2003, 203 tumors in 193 patients aged > or =75 years were treated using SRT (118 T1 tumors, 85 T2 tumors). The median patient age was 79 years, 80% of patients were considered medically inoperable, and 20% of patients declined surgery. The median Charlson comorbidity score was 4, and severe chronic obstructive pulmonary disease (Global Initiative for Chronic Obstructive Lung Disease Class III or greater) was present in 25% of patients. Risk-adapted SRT schemes were used with the same total dose of 60 grays in 3 fractions (33%), 5 fractions (50%), or 8 fractions (17% of patients), depending on the patient's risk for toxicity. SRT was well tolerated, and all but 1 patient completed treatment. Survival rates at 1 year and 3 years were 86% and 45%, respectively. Survival was correlated with performance score (P = .001) and pre-SRT lung function (P = .04). The actuarial local control rate at 3 years was 89%. Acute toxicity was uncommon, and late Radiation Therapy Oncology Group grade > or =3 toxicity was observed in <10% of patients. SRT achieved high local control rates with minimal toxicity in patients aged > or =75 years despite their significant medical comorbidities. These results indicated that more active diagnostic and therapeutic approaches are justified in elderly patients and that SRT should be considered and discussed as a curative treatment alternative.