Background: The purpose of this analysis is to evaluate the effect of institutional accrual volume on clinical outcomes among patients receiving chemoradiation for locally advanced non-small cell lung cancer (LA-NSCLC) on a phase III trial. Methods: Patients with LA-NSCLC were randomly assigned to 60 Gy or 74 Gy radiotherapy (RT) with concurrent carboplatin/paclitaxel +/- cetuximab on NRG Oncology RTOG 0617. Participating institutions were categorized as low-volume centers (LVCs) or high-volume centers (HVCs) according to the number of patients accrued (≤3 vs > 3). All statistical tests were two-sided. Results: Range of accrual for LVCs (n = 195) vs HVCs (n = 300) was 1 to 3 vs 4 to 18 patients. Baseline characteristics were similar between the two cohorts. Treatment at a HVC was associated with statistically significantly longer overall survival (OS) and progression-free survival (PFS) compared with treatment at a LVC (median OS = 26.2 vs 19.8 months; HR = 0.70, 95% CI = 0.56 to 0.88, P =. 002; median PFS: 11.4 vs 9.7 months, HR = 0.80, 95% CI = 0.65-0.99, P =. 04). Patients treated at HVCs were more often treated with intensity-modulated RT (54.0% vs 39.5%, P =. 002), had a lower esophageal dose (mean = 26.1 vs 28.0 Gy, P =. 03), and had a lower heart dose (median = V5 Gy 38.2% vs 54.1%, P =. 006; V50 Gy 3.6% vs 7.3%, P <. 001). Grade 5 adverse events (AEs) (5.3% vs 9.2%, P =. 09) and RT termination because of AEs (1.3% vs 4.1%, P =. 07) were less common among patients treated at HVCs. HVC remained independently associated with longer OS (P =. 03) when accounting for other factors. Conclusion: Treatment at institutions with higher clinical trial accrual volume is associated with longer OS among patients with LA-NSCLC participating in a phase III trial.