Selective estrogen receptor modulators (SERMs) appear to reduce the incidence of breast cancer in high-risk women. Five years of tamoxifen administration after the diagnosis of breast cancer results in a 50% reduction in the incidence of contralateral breast cancer. This reduction is maintained for 5 years after therapy is discontinued. The Study of Tamoxifen And Raloxifene (STAR), presently ongoing, will address the questions of breast cancer prevention, risk of endometrial cancer, the incidence of bone fractures, and coronary artery disease in women treated with these SERMs.