Background: There is significant heterogeneity in the treatment of stage IIIA non–small cell lung cancer (NSCLC). This study evaluated the therapeutic and survival disparities in patients with stage IIIA NSCLC based on the facility volume using the National Cancer Database. Methods: Patients with stage IIIA NSCLC diagnosed from 2004 through 2015 were included. Facilities were classified by tertiles based on mean patients treated per year, with low-volume facilities treating ≤8 patients, intermediate-volume treating 9 to 14 patients, and high-volume treating ≥15 patients. Cox multivariate analysis was used to determine the volume–outcome relationship. Results: Analysis included 83,673 patients treated at 1,319 facilities. Compared with patients treated at low-volume facilities, those treated at high-volume centers were more likely to be treated with surgical (25% vs 18%) and trimodality (12% vs 9%) therapies. In multivariate analysis, facility volume was independently associated with all-cause mortality (P<.0001). Median overall survival by facility volume was 15, 16, and 19 months for low-, intermediate-, and high-volume facilities, respectively (P<.001). Compared with patients treated at high-volume facilities, those treated at intermediate- and low-volume facilities had a significantly higher risk of death (hazard ratio, 1.09 [95% CI, 1.07–1.11] and 1.11 [95% CI, 1.09–1.13], respectively). Conclusions: Patients treated for stage IIIA NSCLC at high-volume facilities were more likely to receive surgical and trimodality therapies and had a significant improvement in survival.