The factors that increase the risk of development of endometrial cancer are reviewed. Many of these conditions are frequently associated with an elevated production of estrone in peripheral (nonendocrine) tissues from circulating androstenedione. Elevated estrone production may occur in young, anovulatory or postmenopausal women whose ovaries secrete higher than normal amounts of androstenedione. Alternatively, conditions such as obesity and liver disease are associated with higher than normal rates of conversion of androstenedione to estrone, resulting in high estrone levels. Neither the exact tissue site(s) of conversion nor the normal function of this process has yet been established. Much less information concerning steroid hormone receptor measurements in endometrial cancer than in breast cancer is available. However, it seems certain that measurement of progesterone receptors will provide a useful guide in the selection of progestational therapy.