Abstract Background Obesity is a known risk factor for developing endometrial cancer. However, the association of obesity with endometrial cancer (EC) outcomes has not been clearly established. This study examined how outcomes in women with early stage EC vary with body composition measured via computed tomography (CT). Methods In this retrospective study, patients diagnosed with EC international Federation of Gynecology and Obstetrics stages I-III and available CT scans were included. Automatica software was used to assess the areas of visceral adipose tissue, subcutaneous adipose tissue (SAT), and intermuscular adipose tissue (IMAT) and skeletal muscle area. Results Of 293 patient charts assessed, 199 met eligibility criteria. Median body mass index (BMI) was 32.8 kg/m2 (interquartile range [IQ] = 26.8-38.9); 61.8% had histologic subtype endometrioid carcinoma. Adjusted for age, international Federation of Gynecology and Obstetrics stage, and histologic subtype, a BMI of at least 30 vs less than 30 kg/m2 was associated with lower endometrial cancer–specific survival (ECSS) (hazard ratio [HR] = 2.32, 95% confidence interval [CI] = 1.27 to 4.25) and overall survival (OS) (HR = 2.7, 95% CI = 1.35 to 5.39). Higher IMAT 75th vs 25th percentile and SAT of at least 225.6 vs less than 225.6 cm2 were associated with lower ECSS (HR = 1.53, 95% CI = 1.1 to 2.13, and HR = 2.57, 95% CI = 1.13 to 5.88) and OS (HR = 1.50, 95% CI = 1.11 to 2.02, and HR = 2.46, 95% CI = 1.2 to 5.01), respectively. The association of visceral adipose tissue (75th vs 25th percentile) with ECSS and OS was not statistically significant (HR = 1.42, 95% CI = 0.91 to 2.22, and HR = 1.24, 95% CI = 0.81 to 1.89). Conclusion Higher BMI, IMAT, and SAT were associated with higher mortality from EC and lower OS. A better understanding of the mechanisms underlying these relationships could inform strategies to improve patient outcomes.