Background: To determine the impact on overall survival (OS) of the sequence-order of adjuvant radiation (RT) and chemotherapy (CT) on different advanced endometrial cancer (EC) histologies. Methods: Stage 3 endometrioid (EAC), serous (SER), clear cell (CC), and carcinosarcoma (CS) patients who underwent primary surgical staging from 1999-2011 were identified in SEER-Medicare. Sequence, timing, and modality of RT and CT were analyzed using Kaplan-Meier estimates, log rank tests, and multivariable cox modeling. Treatment groups with n < 10 were excluded in cox modeling. Results: Of 2375 cases identified (1537 EAC, 485 SER, 96 CC, 257 CS), 31.3% received no AT. The remainder received RT or CT alone, concurrent RT-CT, serial or sandwich modalities (table 1). OS differed by receipt of AT overall as well as within each histologic subtype (log rank p < 0.05, all). After adjusting for age, race, substage, region, and histology, all patients receiving AT except for concurrent RT-CT followed by CT, had improved OS over no treatment (all p < 0.05). However, differences by histology were seen. For EAC the sandwich arm had the greatest reduction in death (72%), whereas for SER and CC the concurrent RT-CT arms fared best. For CS receipt of any CT improved OS, whereas above RT alone did not. (Table1). Conclusions: OS for advanced EC significantly differs by histology and mode of adjuvant therapy. Future studies should evaluate whether sandwich therapy for EAC, concurrent RT-CT for SER and CC, and CT alone for CS may most effectively improve OS.