To examine outcomes in a modern treatment era for stage III uterine serous carcinoma (USC). 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 χ² 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 log-rank test, and Cox proportional hazards. 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/ 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.