A histological study of 15 examples of a unique proliferative and tubular lesion (Fenoglio and Lattes) of the breast was performed. Although it consistently lacked infiltration of adipose tissue, the commonality of some of its morphologic features and those of tubular cancer provokes the possibility that these lesions may represent incipient tubular cancers. Nevertheless, such lesions may be satisfactorily treated by simple excision. Since we are certain only about its topographic and clinical behavior, but not its precise biologic nature, we regard the designation nonencapsulated sclerosing lesion most appropriate. Stromal and periductal elastosis was not infrequently encountered in examples of overt sclerosing and blunt ductal adenosis which may mimic, but can readily be distinguished from, the nonencapsulated sclerosing lesion.