A cohort study of women with ductal involvement by cells of atypical lobular hyperplasia (DIALH) revealed an incidence of 1.4% in benign biopsy specimens. When combined with diagnostic lobular unit alterations of atypical lobular hyperplasia (ALH), a consequent risk of invasive carcinoma of 6.8 times that in the general population was found. This relative risk for women with ALH and DIALH approaches the risk for lobular carcinoma in situ, whereas the risk for ALH with or without DIALH is 4.3 and the risk for ALH without DIALH is reduced to 2.7. Only definitive changes of DIALH with an insinuated characteristic population of cells between attenuated luminal cells and basement membrane should be so diagnosed. DIALH in association with lobular alterations that are borderline with regard to a diagnosis of lobular carcinoma in situ will increase the certainty that a medically meaningful increased risk for subsequent invasive cancer is indicated.