Intrauterine devices (IUDs), long-acting and reversible contraceptives, induce a number of immunological and biochemical changes in the uterine environment that could affect endometrial cancer (EC) risk. We addressed this relationship through a pooled analysis of data collected in the Epidemiology of Endometrial Cancer Consortium. We combined individual-level data from 4 cohort and 14 case-control studies, in total 8,801 EC cases and 15,357 controls. Using multivariable logistic regression, we estimated pooled odds ratios (pooled-ORs) and 95% confidence intervals (CIs) for EC risk associated with ever use, type of device, ages at first and last use, duration of use and time since last use, stratified by study and adjusted for confounders. Ever use of IUDs was inversely related to EC risk (pooled-OR=0.81, 95% CI=0.74-0.90). Compared with never use, reduced risk of EC was observed for inert IUDs (pooled-OR=0.69, 95% CI=0.58-0.82), older age at first use (35 years pooled-OR=0.53, 95% CI=0.43-0.67), older age at last use (45 years pooled-OR=0.60, 95% CI=0.50-0.72), longer duration of use (10 years pooled-OR=0.61, 95% CI=0.52-0.71) and recent use (within 1 year of study entry pooled-OR=0.39, 95% CI=0.30-0.49). Future studies are needed to assess the respective roles of detection biases and biologic effects related to foreign body responses in the endometrium, heavier bleeding (and increased clearance of carcinogenic cells) and localized hormonal changes. What's new? Are IUDs associated with endometrial cancer? Around the world, the intrauterine device is gaining popularity as a long-term birth control strategy. Positioned as it is embedded in the uterine lining, an IUD could affect endometrial tissue. This study builds on previous work by considering the type of device used, in addition to factors such as duration of use. The authors found that women who had used an IUD, particularly an inert IUD, had less risk of endometrial cancer. The longer the device was used, they found, the more the cancer risk decreased.