Background: Use of combined adjuvant chemoradiation (CRT) in treatment of advanced stage endometrial cancer is increasing, but the survival benefit over chemotherapy (CT) or radiation therapy (RT) alone remains unclear. We examined adjuvant treatment patterns and survival associated with CRT for Stage III-IV high-grade endometrial cancer using a large population-based database. Methods: Women 66 years of age or older who underwent primary surgical treatment for Stage III-IV high-grade endometrial cancer between 2000-2011 were identified from the SEER-Medicare database. Demographic and clinical predictors for receipt of adjuvant CRT vs. CT or RT alone were examined using multinomial logistic regression. In addition, overall survival (OS) by adjuvant treatment type, histology (endometrioid vs. non-endometrioid), stage, and age group were examined using Kaplan-Meier estimates and Cox proportional hazards regression. Results: Of the 2,735 eligible women, 13.1% received CRT vs. 42.5% CT alone vs. 13.2% RT alone, and 31.1% received no adjuvant treatment. Hispanic ethnicity, carcinosarcoma, serous histology, and Stage IV disease were significant predictors of receiving CRT over CT alone. Increasing age group, non-Hispanic black race/ethnicity, endometrioid histology, having 3+ comorbidities at the time of surgery, and not being partnered were associated with receiving RT alone over CRT. For Stage III disease, those who received CT (HR 1.30; 95% CI 1.09-1.55) or RT alone (HR 1.34; 95% CI 1.09-1.64) had poorer 5-year OS compared to CRT. In a subgroup analysis, the relative survival benefit of CRT vs. CT was only significant for women < 75 years of age and was more pronounced for endometrioid (HR 1.72; 95% CI 1.22-2.41) vs. non-endometrioid histology (HR 1.22; 95% CI 0.99-1.49). For Stage IV disease, there was no survival difference among those who received CT or RT only compared to CRT regardless of histologic subtypes. Conclusions: Adjuvant CRT was associated with improved OS in elderly women with Stage III high-grade endometrial cancer. This survival benefit was more pronounced for endometrioid histology and women < 75 years of age.