The major hazard of postmenopausal cyclic estrogen therapy is endometrial hyperstimulation. The incidence of hyperplasia is dose dependent; the incidence of carcinoma is both dose and duration dependent. The risk of carcinoma is small. Invasive procedures such as endometrial biopsy to detect those patients with hyperplasia and carcinoma are unlikely to be cost-effective and have other disadvantages. With cyclic estrogens, biopsies should be performed at regular intervals irrespective of the bleeding pattern. The possible alterations to cyclic treatments to reduce the risk of endometrial hyperstimulation have been reviewed; only progestogen addition has been shown to be effective. Maximal effects are obtained when progestogens are added for 12 to 13 days each calendar month. To reduce the risk of side effects, the minimum dose of progestogen should be prescribed, and with the nor-testosterone derivatives, a small dose of norethindrone, approximately 1 mg daily, is as effective as 5 mg daily. The smaller doses cause minimal lipid changes. Interpatient variation in response to the 17-hydroxyprogesterone derivatives can occur, and at high doses, adverse lipid effects have been reported. With sequential estrogen/progestogen therapies, the endometrial histology appears to correlate with the bleeding pattern, thereby, perhaps, obviating the need for biopsy. The development of regimens to induce endometrial atrophy and amenorrhea is suboptimal, and further research is required.