Risk grouping for treatment and follow-up strategy of early stage endometrial cancer is confusing to apply in clinical conditions. We investigated the stage-based prognostic factors for tumor recurrence in stage I endometrial cancer with endometrioid histology (EEC).The medical records of women diagnosed with endometrial adenocarcinoma between 1993 and 2013 were retrospectively reviewed. In 521 patients with International Federation of Gynecology and Obstetrics (FIGO) stage I EEC were included. The baseline patient characteristics were analyzed with the chi-square test and Fisher's exact tests. A multivariate analysis with a Cox proportional hazard model and logistic regression were performed to identify the prognostic factors for recurrence-free survival (RFS) in FIGO stage I EEC.The median follow-up period for the included patients was 74.6 months (3.1-264.9 months). Tumor recurrence occurred in 30 patients (5.8%) with a median time span of 22.85 months (2.2-124.7 months). Only 2 factors among the conventional adverse risk factors, including myometrial invasion and histologic grade, affected tumor recurrence in stage I EEC (P = .003 and P = .003, respectively). Myometrial invasion was an independent prognostic factor for RFS in stage IA EEC via multivariate analysis (P = .005). In stage IB EEC, the histologic grade was an independent prognostic factor for RFS. The median RFS of stage IB EEC was 156.0 months in grade 1, 120.0 months in grade 2, and 105.9 months in grade 3 (P = .006).Within stage I EEC, the prognostic factors for tumor recurrence were different between stages IA and IB. Myometrial invasion comprised the prognostic factor in stage IA, whereas the histologic grade comprised the prognostic factor in stage IB.