The appropriate patient selection for adjuvant radiotherapy after primary surgical therapy of non-small-cell lung cancer (NSCLC) is unclear. Four thousand thirteen patients diagnosed from 1988-1995 in 9 registry areas of the Survival, Epidemiology, and End Results program who received primary surgical therapy for pathologic stage T1-3 N1/2 M0 NSCLC were identified. County-level and patient-specific variables associated with the use of postoperative radiotherapy (PORT) were studied by multivariate logistic regression analysis. Prognostic factors for cause-specific survival (CSS) and overall survival (OS) were determined by Cox multivariate analysis. Overall, 58% of node-positive patients received PORT. Use of PORT was independently associated with younger age, more advanced nodal disease, no prior cancer, less extensive surgery than pneumonectomy, and patient residence close to a radiotherapy facility. In multivariate analysis of the entire node-positive population, there were no differences in OS or CSS with the use of PORT. In the patients with N2 disease, PORT was associated with improved OS (5-year OS: 16% without PORT, 22% with PORT; P = 0.001) and CSS (5-year CSS: 25% without PORT, 30% with PORT; P = 0.02). Additionally, patients with = 4 nodes involved also had an improved survival in association with PORT (5-year OS: 11% without PORT, 18% with PORT; P = 0.001; 5-year CSS: 17% without PORT, 25% with PORT; P = 0.009). Therefore, recognizing the inherent limitations of a retrospective, registry-based analysis, patients with more advanced nodal disease appear to have an improved survival with the use of PORT.