When balancing the benefits of screening women for breast cancer against the harms and costs of such screening, one needs to consider the risk for dying of breast cancer, the relative reduction in that risk that will result from screening women in different age groups, and the harms and costs associated with screening.Seven randomized, controlled trials provide evidence of the relative risk reduction that results from screening women in different age groups; other studies estimate the harms and costs of screening. These studies indicate that the benefit of screening, expressed as the absolute number of lives extended per 1000 women screened, increases with age and that the harm of screening, expressed as the number of follow-up procedures per cancer detected, decreases with age. Thus, the tradeoff between the benefits and the harms and costs of screening is better for older than for younger women. Because there is no clear cut-point for determining when benefits outweigh harms and costs, it is important to involve women in discussions of breast cancer screening. The women who most need to be involved are those for whom the benefits of screening clearly outweigh the harms and costs and those for whom the benefits and the harms and costs constitute a “close call.” For women in both groups, the physician should routinely raise the issue of screening, first eliciting the patient's perceptions and then providing information and discussion about the risk for breast cancer and about the benefits and the harms and costs of screening. Furthermore, the physician should encourage the patient to use her own values to weigh the benefits against the harms and costs, pointing out biases in reasoning and minimizing socioeconomic barriers. Finally, when the benefits obviously outweigh the harms and costs, the physician should make a clear recommendation for screening.