Due to the aging of the US population, the number of women over the age of 50 years, currently more than 40 million, will substantially increase during the next several decades. This will result in increased incidence and cost for the leading causes of mortality and morbidity, ie, heart disease, stroke, cancer, and osteoporosis. Methods complementary to therapy are needed to prevent the anticipated increase in newly diagnosed cases of these diseases, thus improving the quality of life of postmenopausal women. It is timely to question whether estrogen is one such chemical or chemopreventive agent that can prevent (or minimize) these diseases. It has been reported that the use of estrogen by postmenopausal women has beneficial effects on coronary heart disease and osteoporosis but deleterious effects on cancer, most notably endometrial cancer.1 In this issue of the Archives, two articles address the role of estrogen in disease prevention among