Primarily combined radiotherapy and chemotherapy are used to treat unresectable non-small-cell lung cancer; however, the results are not satisfactory. In this study treatment results were retrospectively analyzed and the prognostic factors related to survival were identified. From March 1999 to January 2004, 102 patients with stage IIIA/IIIB non-small-cell lung cancer received definitive radiotherapy with or without chemotherapy. Radiotherapy involved a daily dose of 1.8-2.0 Gy five times a week; 60 Gy was set as the total dose. Maximal chemotherapy was given to patients with normal kidney, liver, and bone marrow functions. The 5-year overall survival rate was 22.2%; the median survival was 18 months. The median follow-up of surviving patients was 53 months. The complete or partial response rate was 85%. At the time of the last follow-up, 21 patients were alive and 81 patients had died, including 5 patients who had died due to radiation pneumonitis. There were significant differences in survival and in the fatal radiation pneumonitis rate between patients with superior lobe lesions and those with middle or inferior lobe lesions. Patients whose primary tumor is located in the superior lobe appear to have a better clinical outcome.