Background: The clinicopathologic significance of lower uterine segment involvement (LUSI) in endometrial cancer patients remains unclear. Although LUSI has been reported to be a prognostic indicator, literature is limited. Methods: We studied 481 surgically staged endometrioid endometrial cancers with disease confined to the uterus (FIGO 1988 stage I or II). Primary outcomes were overall survival (OS) and disease-free survival (DFS). The relationships between LUSI and OS and DFS were assessed using the Kaplan-Meier method and Cox proportional hazard models. The t test or Fisher exact test was used for evaluating relationships between variables of interest. Results: LUSI was present in 223 cases (46.4%), and was associated with both decreased disease free survival (P = 0.02) and overall survival (P = 0.01) in univariate analysis. Multivariate analysis confirmed the association between LUSI and increased risk for recurrence [hazard ratio (HR) 2.27; 95% confidence interval (95% CI) 1.09-4.7; P = 0.03] and increased mortality (HR 1.76; 95% CI 1.12-2.78; P = 0.01). Conclusions: LUSI in patients with early-stage endometrioid endometrial cancer is associated with decreased survival.