The study is based on 112 consecutive mastectomy specimens with carcinoma. Breasts were grossly divided into three basic types: solid, when showing a sizable cone of solid tissue (mammary tissue and fibrous stroma), fatty when almost completely replaced by fat, and intermediary types Ia and Ib. It appears that these types represent stages of an evolutionary process involving the anatomical structure of the breast during life. Mammary alterations gradually lead to lobular atrophy. Generalized lobular atrophy characterizes mainly fatty breasts. Lesions of fibrocystic disease are frequent in breasts of all types. In all three types of breast carcinomas were more frequently located in the outer portion of the breast. Rare locations of carcinomas are associated with the type of breast: a central location is more frequent in fatty, an inner location in intermediary and a diffuse in solid breasts. In fatty breasts irregular tumors are common while in solid breasts tumors without clear borders appear to develop. Multicentric carcinomas were much more frequent in solid breasts than in the other types of breasts. Most multicentric carcinomas are accompanied by multicentric carcinoma in situ. Infiltrative lobular and mixed (lobular-ductal) carcinomas are accompanied by lobular carcinoma in situ, lobular cancerization or both. In infiltrative ductal and the special types of carcinomas the histology of carcinoma in situ differs according to whether or not the infiltrative tumor is single or multicentric. The difference concerns the complete lack of lobular cancerization from cases with single infiltrative tumors.