Endometrial cancer is the most common cancer of the female genital tract in Western countries. Monitoring the incidence is important for health care planning and the identification of risk factors. We present an age-period-cohort analysis of incidence trends of endometrial cancer in Norway from 1953 to 2007 and compare the incidence trends with those in 3 other Nordic countries. Based on the observed trends, we have predicted endometrial cancer rates in Norway in 2015 and 2025. In women at postmenopausal age (≥55 years), the annual incidence increase was 2.1% (95% CI: 0.9%, 3.4%) from 1988 to 1997 and 1.7% (95% CI: 0.6%, 2.8%) from 1998 to 2007. In younger women, there was an annual reduction of 0.6% (95% CI: -2.3%, 2.2%) from 1988 to 1997, followed by an annual increase of 1.7% (95% CI: -0.4%, 3.9%) from 1998 to 2007. The secular changes are likely to reflect both cohort and period effects. Our prediction estimates by 2025 suggest an incidence increase in the range of 50 to 100%, relative to the observed incidence in 2005. There has been a strong and consistent incidence increase in endometrial cancer in the Nordic countries over the last 50 years. The increase has been most pronounced in postmenopausal women, but in the last decade, rates have increased also in women younger than 55 years. The prediction for the next 20 years suggests that endometrial cancer rates will dramatically increase unless effective preventive strategies are implemented.