Objective: Social determinants of health (SDH) have been shown to correlate with adverse cancer outcomes. It is unclear if their impact goes beyond behavioral risk or healthcare access. We aimed to evaluate the association of SDH with endometrial cancer outcomes in a public healthcare system. Design and Setting: A retrospective cohort study of endometrial cancer patients in Ontario, Canada. Population: Women diagnosed with endometrial cancer in Ontario between 2009-2017. Methods: Clinical and sociodemographic variables were extracted from administrative databases. Validated marginalization scores for material deprivation, residential instability and ethnic concentration were used. Associations between marginalization and survival were evaluated using log-rank testing and Cox proportional hazards regression. Results: 20228 women with endometrial cancer were identified. Fewer patients in marginalized communities presented with early disease (70% vs. 76%, p<0.001) and received surgery (89% vs. 93%, p<0.001). Overall survival was shorter among marginalized patients (p<0.001). On multivariable analysis adjusted for patient and disease factors, overall marginalization (HR=1.22, 95% CI 1.03-1.08), material deprivation (HR=1.22, 95% CI 1.10-1.35) and residential instability (HR=1.32, 95% CI 1.19-1.46) were associated with increased risk of death (p<0.001). Conclusions: Socioeconomic marginalization is associated with an increased risk of death in endometrial cancer patients. Targetable events in the cancer care pathway should be identified to improve health equity Funding: This study was supported by a grant (#RD-196) from the Hamilton Health Sciences Juravinski Hospital and Cancer Center Foundation Keywords: uterine cancer, endometrial cancer, social determinants of health