Breast cancer risk assessment in women following a benign breast biopsy is a promising area with regard to intermediate endpoint determination, and has been particularly fostered by the consensus agreement concerning the risk attributed to specific diagnoses [l]. Several recent studies have largely verified this approach 12-41, and a recent report demonstrates general agreement among most expert pathologists regarding diagnostic criteria for these lesions [51. However, in a limited number of cases, determining exact levels of risk for individual patients has been problematic as a result of a failure by pathologists to achieve consensus on diagnostic criteria for these same lesions. This situation has arisen primarily because it is much more tenable to disagree over subjective diagnostic criteria, than it is to argue with robustly supported epidemiological data. Without agreement on reproducible diagnostic criteria, widely promulgated consensus risk estimates for these specific histologic entities are no longer applicable. In addition, those individuals who choose different diagnostic criteria for proliferative breast lesions fail to realize that the terminology, epidemiological risk estimates, and diagnostic criteria used by Dupont and Page are inexorably linked. Since the publication of the consensus statement [l], those using the terms "atypical ductal hyperplasia" and "atypical lobular hyperplasia" have by default accepted the diagnostic criteria of Dupont and Page. Therefore, surgical pathologists who desire to make use of the consensus risk estimates must familiarize themselves with diagnostic criteria for the various histologic entities that comprise proliferative disease of the breast as defined by Dupont and Page [6]. This presentation will concentrate on the importance of a combined histologic and cytologic approach to diagnose proliferative breast lesions, and will specifically focus on usual hyperplasia, atypical ductal hyperplasia, atypical lobular hyperplasia, and both ductal and lobular carcinoma in sifu.