Background: Recent studies have shown that obesity related cancers are increasing in incidence in the US as the rates of obesity rise and some cancers, like colorectal cancer, are occurring in younger age groups. We studied trends in incidence of endometrial cancer (EC), one of the obesity related cancers, in a population wide analysis. Methods: We analyzed data from all cases of EC between 2000 and 2015 from 18 US cancer registries using the National Cancer Institute’s Surveillance, Epidemiology and End Results Program. SEER*Stat was used to query the database for annual percent changes (APC), incidence ratios and percent change in incidence across different age groups, years of diagnosis, histologic subtypes, grade and race. We also studied the reported rates and trends of obesity in the US. Results: APC of age-adjusted EC incidence between 2000 and 2015 was +0.9% (95% confidence interval (CI) 1.1-0.6, p value<0.05). Incidence of EC rose from 17.8 per 100,000 to 19.7 per 100,000 during the same duration. APC for EC incidence for age groups 20-39 and >40 were +3.2% (p-value <0.05) and +0.8% (p value <0.05), respectively. For the age-group 20-39, endometrioid EC was the only histologic subtype that rose in incidence, with an APC of +5.5% and absolute percentage change of 156%. The APC of EC in 20-39 age group was more for whites (3.5%, p-value<0.05) and Asians (2.2%, p-value<0.05) than blacks (1.8, p-value <0.05). CDC reported an increase in obesity rates in adults from 30.5% in 2000 to 37.7% in 2014. Table shows trends of EC incidence in age groups 20-39 and >40 years across various histologic subtypes. (Abbreviations: S significant, NS not significant, NC non-calculable). Conclusions: Endometrial cancer, especially of endometrioid histology, is increasing in incidence and is occurring more often in the younger population. The concomitant rise in obesity rates during the same period point towards a possible causality of the increased in incidence of EC. Population based strategies are needed to decrease the trends in obesity so as to decrease the risk of endometrial cancer in younger women.