Purpose: To evaluate the results and prognostic factors for postoperative adjuvant radiation therapy in patients at stages I and II of endometrial cancer. Materials and Methods: Between January 1991 and December 2006, 35 patients with FIGO stages I and II disease, who received adjuvant radiation therapy following surgery for endometrial cancer at Ewha Womans University Hospital, were enrolled in this study. A total of 17 patients received postoperative pelvic external beam radiation therapy; whereas, 12 patients received vaginal brachytherapy alone, and 6 patients received both pelvic radiation therapy and vaginal brachytherapy. Results: The median follow-up period for all patients was 54 months. The 5-yr overall survival and disease-free survival rates for all patients were 91.4% and 81.7%, respectively. The 5-yr overall survival rates for low-risk, intermediate-risk, and high-risk groups were 100%, 100% and 55.6%, respectively. In addition, the 5-yr disease-free survival rates were 100%, 70.0%, and 45.7%, respectively. Although no locoregional relapses were identified, distant metastases were observed in 5 patients (14%). The most common site of distant metastases was the lung, followed by bone, liver, adrenal gland, and peritoneum. A univariate analysis revealed a significant correlation between distant metastases and risk-group (p=0.018), pathology type (p=0.001), and grade (p=0.019). A multivariate analysis also revealed that distant metastases were correlated with pathology type (p=0.009). Papillary, serous and clear cell carcinoma cases demonstrated a poor patient survival rate compared to cases of endometrioid adenocarcinoma or adenosquamous carcinoma. The most common complication of pelvic external beam radiation therapy was enteritis (30%), followed by proctitis, leucopenia, and lymphedema. All these complications were of RTOG grades 1 and 2; no grades 3 and 4 were observed. Conclusion: For the low-risk and intermediate-risk groups (stages 1 and 2) endometrial cancer, pelvic control, and overall survival rate was free of severe toxicity when pelvic radiation therapy or vaginal brachytherapy was performed. In the high-risk group, pelvic control rate was excellent, but the survival rate was poor due to distant metastases, in spite of the pelvic radiation therapy. The combined modality of chemotherapy and radiation therapy is recommended for high-risk groups. For the intermediate-risk group, a prospective randomized study is required to compare the efficacy between whole pelvic radiation therapy and vaginal brachytherapy.