Coronary heart disease (CHD) is the leading cause of death in women. Epidemiologic, mechanistic, and animal-model studies have produced convincing evidence that hormone replacement therapy (HRT) could substantially decrease rates of CHD in women. However, several randomized clinical trials of HRT in women with CHD have been unable to confirm the earlier suggestions of benefit, and there has even been a suggestion of increased CHD risk. This article will review the findings to date of these long-term randomized clinical trials of HRT for prevention or treatment of CHD.