The occurrence of cancer of the corpus uteri in Denmark is examined by the use of data from the Danish Cancer Registry. The study population consists of 14,149 cases diagnosed with cancer of the corpus uteri between 1943 and 1980. Since 1943, the incidence has been steadily increasing. The trend in the incidence rates varies in different age groups, and examination of birth cohorts shows higher rates after the age of 50 for more recent generations. The trend is evaluated in relationship to changes in diagnostic practices and to changes in prevalence of risk factors. Of the latter, estrogen use is considered a plausible explanation for the increasing incidence in women aged 55-64 years Correction of the age-specific incidence rates for hysterectomy reveals a pattern very similar to that of breast cancer.