To determine whether risk of endometrial cancer among women with type 2 diabetes differs with respect to other endometrial cancer risk factors, the authors used data from a population-based case-control study (1,303 cases and 1,779 controls) conducted in western Washington State during 1985-1999. History of type 2 diabetes was associated with endometrial cancer (odds ratio (OR) = 1.7, 95% confidence interval (CI): 1.2, 2.3), more strongly among women with a recent diabetes diagnosis (<5 years) (OR = 2.6, CI: 1.5, 4.7) than among those with a more distant diagnosis (> or =5 years) (OR = 1.3, CI: 0.8, 1.9). Type 2 diabetes was associated with endometrial cancer among women with a body mass index (BMI) (weight (kg)/height (m)(2)) less than 35 but not among women with a BMI of 35 or more. The observed associations persisted after finer adjustment for BMI to control for residual confounding. History of diabetes was associated with a twofold increased risk of endometrial cancer among hypertensive women, but no association was observed among nonhypertensive women. The risk associated with type 2 diabetes appeared not to vary greatly with respect to other endometrial cancer risk factors. These results support the hypothesis that type 2 diabetes is associated with endometrial cancer irrespective of the presence of other risk factors for this disease, except possibly hypertension and extreme obesity.