Objective: To examine outcomes in a modern treatment era for stage III uterine serous carcinoma (USC). Methods: Fifty women were retrospectively identified as 2009 International Federation of Gynecology and Obstetrics stage III USC patients who received radiotherapy (RT) at our institution between 1/2003-5/2018. The patients were divided into 2 cohorts: 20 in the early era (2003-2010) and 30 in the modern era (2011-2018). Patient characteristics were compared using χ 2 tests for categorical variables and t-tests for continuous variables. Recurrence free survival (RFS) and overall survival (OS) were analyzed with Kaplan-Meier estimates, the logrank test, and Cox proportional hazards. Results: The modern era differed from the early era in the increased use of volume-directed external beam RT (EBRT) as opposed to vaginal brachytherapy (VB) alone (33.3% vs 5.0%, p=0.048), minimally invasive surgery (56.7% vs. 25%, p=0.027), sentinel node sampling (26.7% vs. 0%, p=0.012), computed tomography imaging in the perioperative period (63.3% vs. 30%, p=0.044), and human epidermal growth factor receptor 2/neu testing (96.7% vs. 55%, p=0.001). Median follow-up for early and modern eras was 37.27 and 33.23 months, respectively. The early vs. modern 3-year RFS was 33% and 64% (p=0.039), respectively, while the 3-year OS was 55% and 90% (p=0.034). Regional nodal recurrence more common among the patients who received VB only (p=0.048). Conclusion: Modern era treatment was associated with improved RFS and OS in patients with stage III USC. Regional nodal recurrences were significantly reduced in patients who received EBRT.