The breast duct patterns and radiographic density, or dysplasia, of 104 breast cancer patients in Hawaii were examined by mammography. The proportions of the four types of breast structure were analyzed for possible relation with age, menopausal state, height, weight, and race. Multiple regression analysis indicated that menopausal state appears to be more important than age per se for the general change in breast structure. Low body weight, but not race, is associated with prominent duct patterns and dysplasia.