The authors have studied breast cancer in fatty breasts in an attempt to prove their observations that Wolfe's classification "N1" on mammography was not necessarily "normal". Two groups of women, the first called group "A" consisting of 384 women with cancer of the breast, and group "B", the control group of 400 women who had no abnormality in the breast, were studied and correlated for epidemiological, thermographic, mammographic, and anatomo-pathological parameters. The following epidemiological factors were studied: age, marital status, profession, age at menarche and at menopause, menstrual behaviour, age at the first pregnancy that went to term, parity (live and still births), type of delivery, length of breast feeding, number of abortions, use of hormones, and family history of cancer of the breast. In the thermographic studies: the topography of the heat pattern, the primary pathological signs and the thermic state were studied. In mammography: the mammographic appearance after Wolfe and the presence of microcalcifications was studied. In group "A" the following histological group parameters were studied: which breast, in which quadrant the nodule was situated, the type of breast the contour and size of the tumour, the number of axillary nodes removed, the histological type of the cancer, the histological grade of the malignancy, vascular invasion, details about the skin and the areola, calcifications, lymphocytic infiltration of the stroma, multicentricity, the co-existence of cystic disease of the breast and invasion of the axillary nodes. All these above-mentioned parameters were correlated with: the age, the existence of previous pregnancies at term, the macroscopic type of the breast and the mammographic type according to Wolfe. The breasts were divided into three macroscopic types: fatty, fibrous and intermediate. The correlation of the mammographic type according to Wolfe showed that types N1 and P1 corresponded to fatty and partially intermediate types. In group "A" the macroscopically fatty as compared with the other type of breasts showed a more extensive degree of infiltrations: vascular (76.5%), skin (90.3%), areolae (88.9%) and lymphocytic (80.1%), as well as a higher percentage of axillary metastases (57.7%).