BACKGROUND: To the authors' knowledge, optimal adjuvant approaches for resected duodenal adenocarcinoma are not well established. Given the significant risk of locoregional disease recurrence, there may be a subset of patients who demonstrate an improvement in overall survival (OS) from the addition of radiotherapy (chemoradiotherapy [CRT]) to an adjuvant chemotherapy regimen. METHODS: Patients with resected, nonmetastatic duodenal adenocarcinoma who received chemotherapy (694 patients) or CRT (550 patients) were identified in the National Cancer Data Base (1998-2012). Cox regression identified covariates associated with OS. The chemotherapy and CRT cohorts were matched (1:1) by propensity scores based on the likelihood of receiving CRT or the survival hazard from Cox modeling. OS was compared using Kaplan-Meier estimates. RESULTS: CRT was more frequently used for patients who underwent positive-margin surgical resection (15.9% vs 9.1%; P<.001). At a median follow-up of 79.2 months (interquartile range, 52.9-114.9 months), the median OS of the propensity score-matched cohort was 46.7 months (interquartile range, 18.9 months to not reached). No survival advantage was observed for patients who were treated with adjuvant CRT compared with those treated with adjuvant chemotherapy (median OS: 48.9 months vs 43.5 months [HR, 1.04; 95% confidence interval, 0.88-1.22 (P = .669)]). CRT was not found to be associated with a significant improvement in the median OS after positive-margin surgical resection (133 patients; 27.6 months vs 18.5 months [P = .210]) or in the presence of T4 classification (461 patients; 30.6 months vs 30.4 months [P = .844]) inadequate lymph node staging (584 patients; 40.5 months vs 43.2 months [P = .707]), lymph node positivity (647 patients; 38.3 months vs 34.1 months [P = .622]), or poorly differentiated histology (429 patients; 46.6 months vs 35.7 months [P = .434]). CONCLUSIONS: The addition of radiation to adjuvant therapy does not appear to significantly improve survival, even in high-risk cases. Cancer 2017;123:967-76. © 2016 American Cancer Society.