The debate about breast cancer screening for women in their 40s has become so contentious that effective communication and rational discussion on this topic have been compromised. This contentiousness might be defused by understanding the reasons for it. The debate is less about facts than it is about perceptions and values. There is disagreement about how to fairly describe facts about risk and how to avoid misperceptions that may distort assessment of risk. Other sources of disagreement concern the potential harms of screening, the relative roles of physicians and patients in decision making, and how to factor cost into screening decisions. The entire decision-making process has also been highly charged by single-issue advocacy groups and a kind of gender rivalry. Several approaches might help defuse the debate and improve discussion. First, those on both sides of the debate might agree on several things: 1) that the evidence from clinical trials is widely agreed-upon and thus that a main task now is to factor in the values of individual women who are making decisions; 2) that the values of women may differ substantially and that those differences should be respected; 3) that both individuals and the public should be fully and fairly informed about the pros and cons of screening; and 4) that cost-effectiveness should at least be considered during the decision-making process. Lessons from this debate may apply to other medical problems that have small degrees of risk and whose management is strongly debated.