Many physicians consider the prognosis exceptionally poor for patients with localized non-small cell lung cancer who are not eligible for surgery, either because of the extent of their disease or because a coexisting medical condition precludes surgery. Thus, these patients frequently are not offered aggressive curative therapy. However, the disease of many of these patients is potentially curable and should be considered for curative treatment. Although pathologic data from surgical specimens are useful in predicting prognosis, many prognostic factors have also been identified for medically inoperable and locally advanced, unresectable disease. Several of these prognostic factors can and should be used clinically to estimate the risk of lymph node involvement within the clinically uninvolved mediastinum, thereby aiding in the design of radiation therapy fields, and to estimate prognosis, thereby helping to determine which patients should be offered aggressive therapy with curative intent. (C) 2000 by W.B. Saunders Company.