A cohort of 1192 patients with endometrial carcinoma were followed up to determine the frequency of other malignancies among them. The incidence rate of all types of cancer was not greater than in the general population. The relative risk of breast cancer after endometrial carcinoma was 1.3 times population rates. This increase, however, was confined to those who shared risk factors common to breast cancer--that is, nulliparity and, to a lesser extent, obesity. The parous, nonobese patient with endometrial carcinoma was not found to be at increased risk of subsequent breast cancer. An unusual occurrence of primary adenocarcinoma of the lung was found ten or more years after treatment for endometrial carcinoma. This increase was not associated with cigarette smoking.