Large numbers of observational studies have described a decrease in the incidence of cardiovascular disease in women taking hormone replacement therapy (HRT). The potential mechanisms for this effect are numerous, including direct effects on lipid levels and lipid metabolism, cardiovascular dynamics, and endothelial reactivity. The beneficial effects of HRT are probably affected by various factors, including the age of onset of therapy, the presence of coronary artery disease, the type of estrogen and whether it is used in combination with progesterone, concurrent modification of other cardiac risk factors, and duration of therapy. Until further prospective clinical trials are done, HRT should be considered in those women for whom the potential benefits exceed the potential risks, on the basis of an individualized patient evaluation.