Although surgery has traditionally been the treatment of choice for patients with resectable non-small cell lung cancer, for those with significant medical problems where surgery is contraindicated, radiation therapy (RT) is a reasonable treatment modality. In contrast to the widely held belief that RT confers little benefit to these patients, a review of the literature and our own series of 245 patients shows that RT can provide significant tumor shrinkage, improved symptoms, and in a small but not negligible number of patients, cure. Several prognostic factors have emerged, including patient performance status, prior weight loss, tumor size, and radiation dose. Patients with a good performance status and a small tumor treated to a dose of 65 Gy or more have a real possibility of long-term survival and cure. Larger tumors demand strategies to improve the therapeutic ratio, such as hyperfractionation, conformal RT, brachytherapy boosts, or chemotherapy. Patients with medically inoperable lung cancer should be offered RT with curative intent, rather than the option of no treatment.