Specific, combined histologic and cytologic patterns of atypical epithelial hyperplasia (AH) in the breast indicate a medically relevant risk of breast cancer development in 5% to 10% of women with otherwise benign biopsies. This risk is four to five times that of similar women without such lesions, that is, women of the same age and at risk for the same period of time. These relative risks are not stable and fall 10 to 15 years after detection, more closely approximating the risks of women of comparable age. Proliferative disease without atypia, no matter how extensive or complex, predicts only a slight elevation of risk, which approaches double that of the reference population. There is a strong interaction of AH with family history of breast cancer in at least a first degree relative. This risk doubles the risk of AH alone and is approximately 20% at 10 to 15 years after biopsy, particularly for women in their forties and early fifties. These considerations are of less clinical importance in women over age 60. Low replacement doses of conjugated estrogen after the menopause do not further elevate risk beyond that identified by histologic patterns. Non-comedo ductal carcinoma in situ may be considered a true precursor lesion; however, it differs significantly in many ways from the more advanced lesion recognized as the comedo type of ductal carcinoma in situ. Small examples of noncomedo ductal carcinoma in situ can eventuate in invasive carcinoma after 6 to 10 years. They may be treated by wide local excision without radiation, with no recurrence up to 8 to 10 years in all likelihood. Ductal carcinoma in situ lesions can be extensive within the breast, and this conservative posture should be reserved for smaller lesions.