Purpose: The North Central Cancer Treatment Group performed a phase III trial to determine whether chemotherapy plus either bid radiation therapy (RT) or daily (qd) RT resulted in a better outcome for patients with stage III non-small-cell lung cancer (NSCLC). No difference in survival was identified between the two arms. This secondary analysis was performed to examine the relationship between patient age and outcome. Patients and Methods: Two hundred forty-six patients were randomized to receive etoposide plus cisplatin and either RT qd or split-course RT bid. This retrospective study compared the outcomes of patients aged ≥70 years ("elderly patients") with those of younger individuals. Of the 244 assessable patients, 63 (26%) were elderly, and 181 (74%) were younger individuals. Results: The 2-year and 5-year survival rates were 39% and 18%, respectively, in patients younger than 70 years, compared with 36% and 13%, respectively, in elderly patients (P = .4). Grade 4+ toxicity occurred in 62% of patients younger than 70 years compared with 81% of elderly patients (P = .007). Grade 4+ hematologic toxicity occurred in 56% of patients younger than 70 years, compared with 78% of elderly patients (P = .003). Grade 4+ pneumonitis occurred in 1% of those younger than 70 years, compared with 6% of elderly patients (P = .02). Conclusion: Toxicity, especially myelosuppression and pneumonitis, was more pronounced in the elderly patients receiving combined-modality therapy for locally advanced NSCLC. Despite increased toxicity, elderly patients have survival rates equivalent to younger individuals. Therefore, fit, elderly patients with locally advanced NSCLC should be encouraged to receive combined-modality therapy, preferably on clinical trials with cautious, judicious monitoring. Future studies should explore ways to decrease toxicity of therapy in elderly patients. © 2003 by American Society of Clinical Oncology.