In order to define cancer of the breast limited to the breast parenchyma 114 infiltrating carcinomas with a maximum size of 1 cm and 88 non-infiltrating carcinomas (without size limitation) were investigated histologically for axillary lymph node metastases. All carcinomas with a size of up to 0.5 cm (25 cases) were free of lymph node metastases. Infiltrating carcinomas with a size of more than 0.5 cm up to 1 cm (108 cases) showed metastases in 25%. Non-infiltrating carcinomas of more than 0.5 cm (69 cases) had lymph node metastases in 1.4%. Considering the excellent prognosis, by histologically criteria infiltrating carcinomas of up to 0.5 cm and all non-infiltrating carcinomas can be considered as cases of "early breast cancer". For detection of these carcinomas mammography is of considerable importance, particularly when micro-calcifications are demonstrated. Among non-invasive carcinomas 74% were thus discovered by this method.