Adjuvant tamoxifen therapy is associated with modest improvement in disease-free and overall survival in women with invasive axillary node-negative breast cancer. The preponderance of data supporting these general conclusions are from trials in postmenopausal women; in premenopausal women data appear convincing regarding disease-free, hut not overall, survival. Firm conclusions regarding magnitude of benefit related to presence of different prognostic factors cannot be drawn at present.In postmenopausal women tamoxifen appears to alter favorably some risk factors for cardiovascular diseases and osteoporosis, which are the most common causes of mortality or morbidity in older American women. Adjuvant tamoxifen is associated with a significantly reduced risk of second primary breast cancer. Major serious risks of tamoxifen therapy include depression, and possibly thrombophlebitis and uterine endometrial cancer. Symptomatic vasomotor and gynecological side effects are frequent. Decision making with women should include assessment of these multisystem benefits and risks.