Although there is a slightly increased risk of endometrial cancer from estrogen therapy for menopausal women, progestogens given along with the estrogen significantly decrease the incidence of this malignancy to a rate lower than that of untreated women. Postmenopausal women predisposed to adenocarcinoma of the endometrium because of increased endogenous estrogens can be identified with the progestogen challenge test and treated with cyclic progestogens for 10 days each month to prevent endometrial cancer. Oral contraceptives containing both estrogens and progestogens in each tablet are protective against developing adenocarcinoma of the endometrium, whereas the sequential birth control pills provided less protection. The incidence of breast cancer is significantly lower in both estrogen and estrogen-progestogen users than in postmenopausal women never using these hormones. In those women found to have breast cancer while using these hormones, the prognosis is better than that found in women never exposed to exogenous estrogens, most likely due to an earlier detection. No clear-cut pattern of either abnormal hormone production or milieu has been found in women with carcinoma of the breast. Oral contraceptives reduce the risk of benign breast disease and afford some protection from the subsequent development of breast cancer. The mortality rate from breast cancer developing in oral contraceptive users is significantly lower than that of the non-users.