The effects of estrogen, progestogens, and combination steroids on the endometrium and cervix are reviewed. Prolonged administration of estrogen or sustained production of unopposed endogenous estrogenic substances may be associated with an increased risk of endometrial hyperpfasia and atypical adenomatous hyperplasia leading to well‐differentiated adenocarcinoma of the endometrium. The development of endometrial cancer does not seem to depend on the presence of the ovaries or the administration of estrogen, since the cancer is known to occur in women with dysgenetic ovaries and in surgical castrates who have never received exogenous estrogen. Endogenous estrone appears to play a role in the genesis of endometrial cancer and its precise function needs to be investigated.