Background: Locally advanced endometrioid adenocarcinoma (EAC) is an aggressive disease with the potential of metastatic spread and local recurrence after initial surgical resection. Adjuvant treatment often includes a combination of chemotherapy (CTx) and/or radiation therapy (RT). GOG 122 showed that adjuvant chemotherapy was important in preventing recurrence for locally advanced EAC. Other studies for carcinosarcoma and serous papillary tumors of the uterus showed improved outcomes using an adjuvant ”sandwich” chemoradiation (CRT) regimen, splitting CTx before and after RT. We retrospectively review patients treated postoperatively with the ”sandwich” regimen for FIGO stage III endometrioid adenocarcinoma. Methods: Thirty-four patients with FIGO stage III EAC were treated between 2008-2016 with the “sandwich” regimen: 1) 3 cycles of carboplatin (AUC 6)and paclitaxel 175 mg/m²; 2) RT (45Gy in 25 fractions) to the pelvis and, when indicated, to the para-aortic lymph nodes, and vaginal brachytherapy (15 Gy in 3 fractions prescribed to 0.5 cm vaginal depth); 3) 3 more cycles of carboplatin (AUC 5) and paclitaxel. Patients who received less than 4 cycles of CTx were excluded. Intensity modulated radiation therapy (IMRT) was used to reduce normal tissue toxicity. Results: Median follow-up was 3.1 years. All patients completed the prescribed RT. Twenty-nine patients completed 6 cycles of chemotherapy, 3 finished 5 cycles, and 2 finished 4 cycles due to toxicity. Grade 3-4 hematologic toxicity was seen in 19 (56%) patients. Acute gastrointestinal toxicity of grade ≥ 2 was reported in 4 (12%) patients. There was no reported acute genitourinary toxicity of grade ≥ 2. Grade 2 vaginal stenosis was seen in 5 (15%) patients. Actuarial progression-free survival at 3 and 5 years was 84.1% and 59.8%, respectively. Actuarial overall survival at 3 and 5 years was 88% and 77%, respectively. Conclusions: Adjuvant IMRT “sandwiched” between carboplatin/paclitaxel CTx for FIGO stage III EAC is well tolerated, with the worst toxicity being hematologic. This regimen also provides a good overall survival at 5 years, though lower PFS shows that there are patients living with evidence of disease.