The Korean Gynecologic Oncology Group (KGOG) undertook a multi-center retrospective study to develop a preoperative prediction model for lymph node metastasis in endometrial cancer (KGOG-2014). This retrospective multi-center study showed that the accurate identification of a low-risk group for lymph node metastasis among the patients with endometrial cancer can be achieved with the new criteria using preoperative MRI and serum CA-125 assay. In this study, serum CA125 levels and three MRI parameters (deep myometrial invasion, lymph node enlargement, and extension beyond uterine corpus) were found to be independent risk factors for nodal metastasis. Based on the success of KGOG-2014, Korean Gynecologic Oncology Group initiated this prospective, multi-center observational study to validate our prior prediction model.