Using computerized image analysis, we newly devised a method for automatic quantitative evaluation of nuclear arrangements in variable proliferative intraductal (cribriform) lesions of the breast, by calculating angles of longest nuclear diameter to a horizon (LNDA). Internuclear correlation in the cribriform lesions was thus examined, comparing 22 benign and 62 malignant cases. In the malignant lesions, nuclear arrangements tended to be multidirectional, probably because of vertical nuclear arrangements toward acinar lumens as reflected by the wide distribution of LNDAs. Conversely, in the benign lesions, groups of nuclei tended to arrange toward one certain direction, forming a complex streaming pattern with the distribution of LNDAs usually producing a distinctive peak. Other conventional nuclear features, such as nuclear area, nuclear perimeter, shortest nuclear diameter (SND), and leading variables were also quantitatively assessed for multivariate analysis. It was noted that nuclear arrangements could represent a favorable discriminator. Linear discriminant function could classify 66 of the total 84 cases (78.6%) as being consistent with the diagnosis of pathologists. We conclude that internuclear arrangement could be a useful discriminating variable in benign and malignant breast lesions for the further development of an automatic analytic system.