Women who test positive for a genetic breast cancer marker may have more than a 50% chance of developing the disease. Although past screening technologies have sought to identify actual breast cancers, as opposed to predisposition, the history of screening may help predict the societal response to genetic testing. For decades, educational messages have encouraged women to find breast cancers as early as possible. Such messages have fostered the popular assumption that immediately discovered and treated breast cancers are necessarily more curable. Research, however, has shown that screening improves the prognosis of some--but not all--breast cancers, and also that it may lead to unnecessary interventions. The dichotomy between the advertised value of early detection and its actual utility has caused particular controversy in the United States, where the cultural climate emphasizes the importance of obtaining all possible medical information and acting on it. Early detection has probably helped to lower overall breast cancer mortality. But it has proven hard to praise aggressive screening without exaggerating its merits. Women considering genetic breast cancer testing should weight the benefits and limitations of early knowledge.