There are two approaches to the detection and treatment of breast cancer. Almost all current efforts are focused on improving the detection of small cancers and their treatment. Breast cancers, even when detected at their smallest visible size, still carry a substantial risk of claiming the life of a patient. The alternative is to focus on the identification of cancer precursor lesions. Effective identification and treatment of precursor lesions would prevent all breast cancer deaths. This requires scientific assessment of the effectiveness of prevention strategies in high-risk women. Certain groups of women are known to be at high risk for development of breast cancer. These include women with a personal and/or family history of previous breast cancer, women carrying certain genes, and women with atypical hyperplasia. Detection of atypical hyperplasia by surgical biopsy in a symptomatic population for risk assessment is not practical. The alternative is the use of noninvasive procedures such as fine-needle aspiration biopsy in order to sample and monitor the earliest changes associated with breast cancer. This requires adequate recognition of the cytomorphology of breast cancer precursor lesions and the ability to distinguish between prognostically relevant morphologic alterations and atypias associated with various benign breast diseases.