Cardiovascular diseases remain the leading cause of death in American women. Evidence from epidemiological studies indicates that estrogen replacement therapy in postmenopausal women can reduce their risk of coronary heart disease. Current users, in particular, appear to enjoy the most substantial cardiac benefits. It remains possible that the protective effect of estrogen observed in these studies may be due, in part, to bias. Women who use estrogen see a physician regularly, and compliance with estrogen therapy may identify a low-risk group of women. Furthermore, women who choose to use estrogen may lead generally healthier lifestyles than those who do not take such medication. However, adjustment for known cardiac risk factors in many of the large studies had little impact on the results, implying an equivalent risk status for users and nonusers. In addition, both animal and human studies show that estrogen use lowers low-density lipoprotein cholesterol levels, increases high-density lipoprotein cholesterol levels, improves blood flow, and reduces atherosclerosis. The effect of progestin added to estrogen therapy has not been adequately assessed, but initial evidence suggests that it may somewhat attenuate, although not completely eliminate, the benefits of estrogen on cardiovascular disease. Finally, each individual woman differs in her particular risks and benefits, and careful consideration of each woman's unique situation is required; the fear of breast cancer should be considered, together with the knowledge that many interventions are available to reduce the risk of cardiovascular disease.