Millions of menopausal women are taking hormone supplements. Observational studies suggest that unopposed estrogens reduce the risk of cardiovascular disease and fractures and increase the risk of endometrial cancer and, possibly, breast cancer. In the absence of information from randomized trials, how much of the apparent beneficial effect on heart disease is due to the tendency of healthier women to use these drugs is unknown. The effect on the cardiovascular system of estrogen taken with a progestin is unknown, and this regimen may increase the risk of breast cancer. An approach to health and illness that focuses on a single cause or preventive and on single organ systems is severely limited. Alternative ways to improve cardiovascular and skeletal health that do not increase the risk of cancer are available. A reconsideration of the appropriate use of hormone supplements is needed.