The National Cancer Institute has created a breast cancer risk assessment tool that quickly estimates a woman's individualized absolute risk of developing breast cancer. Understanding the magnitude of risk is important because recent data show that breast cancer incidence may be reduced. All women may improve their overall health and thus perhaps minimize breast cancer risk by maintaining a healthy weight, avoiding cigarettes, limiting alcohol consumption, getting regular exercise, and avoiding non-diagnostic ionizing radiation. Nevertheless, no lifestyle modifications have yet been proven to prevent or definitively lower the risk of breast cancer. In addition, women whose personal breast cancer risk is high may consider reducing risk by pharmacologic or surgical means. In such women, a five-year course of tamoxifen reduced the risk of invasive breast cancer by 49%; women with lobular carcinoma in situ or atypical hyperplasia experienced even greater risk reductions. Because of the potential for vascular and endometrial side effects, women who are candidates for a preventive course of tamoxifen must be counseled regarding its relative risks and benefits. Prophylactic mastectomy offers at least a 90% reduction in the risk of breast cancer, but the physical and psychological changes involved in such a procedure make it a difficult choice for many women. Breast cancer risk assessment and appropriate counseling are becoming standard components of breast cancer screening and overall health maintenance.