In mammary lobular carcinoma three forms of ductular tumor extension have been described that are not strictly confined to the proper glandular lobule. These are the clear pagetoid cells adherent to the basement membrane of small ducts and by some authors seen in relation with microcalcifications. Then there are clover-shaped or saccular changes of the ducts and finally solid or papillary intraductal tumor extensions not always neatly distinguishable from mammary dysplasia. Both for theur diagnostic significance of the main lesion as for the estimation of their prognostic value, the incidence of these findings was reviewed in 72 own cases, 29 of which wewre lobular carcinomas in situ an 43 lobular infiltrating carcinomas. The mentioned findings were seen in 89,9%. The hyperplastic sacular pattern predominated (82 and 67%), followed by pagetoid cells (58 and 47%) not associable with microcalcifications. The solid intraductal tumor extensions were observed in 43 and 17% although aldo in the present material this change was difficult to differentiated from epitheliosis and papillomatosis. The high incidence of these assocaited findings sustains their diagnostic significance when found in an isolated form at indicating the highly probable vicinity of a lobular carcinoma. No prognostic conclusion could be drawn with regard to a major or minor biological aggressiveness.