Most patients who have lung cancer will receive radiation therapy at some point during the course of their disease. For patients with non-small-cell lung cancer, radiation therapy is sometimes used after complete resection, particularly in patients with lymph node involvement. In addition, irradiation is commonly used after incomplete resection. In patients with unresectable non-small-cell lung cancer, radiation therapy alone is typically used, although recent studies of a combination of chemotherapy and radiation therapy, or radiation therapy given in twice-daily fractions, have yielded promising results. For patients with small-cell lung cancer who have limited (that is, nonmetastatic) disease, the addition of thoracic radiation therapy to chemotherapy has improved survival over that with chemotherapy only. The role of prophylactic cranial irradiation in small-cell lung cancer remains controversial. Radiation therapy has a major role in the management of locally recurrent and metastatic lung cancer. Both the bones and the brain are common metastatic sites in patients with lung cancer. Radiation therapy provides effective palliation of symptoms from these and other metastatic lesions. © 1993, Mayo Foundation for Medical Education and Research. All rights reserved.