Evidence from clinical follow-up studies has indicated that there is a relationship between the presence of histologically proven benign breast disease and breast cancer risk and that the level of risk varies according to the histologic category of benign breast disease. In particular, proliferative lesions without atypia are associated with a 1.5- to 2-fold increase in risk, whereas atypical hyperplasias are associated with a fourfold to fivefold increase in breast cancer risk. A number of clinical factors appear to modify the risk associated with these lesions, including the time since biopsy, menopausal status, and family history of breast cancer. Recent studies have begun to evaluate the potential role of biologic, molecular, and genetic markers in assessing breast cancer risk in patients with benign breast disease. Additional information derived from clinicopathologic follow-up studies, epidemiologic studies, and molecular and genetic studies will provide new insights into benign breast disease and breast cancer risk.