Globally, breast cancer is the third most common form of cancer and the most common among women. The age-adjusted incidence rates of breast cancer are 176% higher in developed than in developing nations. Male breast cancer is rare, but important studies provided risk factor information for comparison with studies of female breast cancer. There has been considerable interest in a possible role of organochlorines and polychlorinated biphenyls in the etiology of breast cancer, but the results of several null studies indicate the likelihood of such associations is extremely remote, providing reassuring news for the public. Prophylactic mastectomy was observed to significantly reduce a woman's chances of developing breast cancer, but it does not lower the risk to zero. Tamoxifen was found to be an effective chemopreventive agent in the Breast Cancer Prevention Trial, but this result was not replicated in two randomized trials in Europe. Striking reductions in the risk for breast cancer were observed for raloxifene in a randomized, placebo-controlled trial that had been designed for the prevention of osteoporosis. A large-scale, randomized trial of tamoxifen-verus-raloxifene among women at increased risk for developing breast cancer is now underway.