Clinical and pathologic staging of breast cancer are discussed. A new pathologic staging system is presented: numerical scores are assigned, in cases of infiltrating ductal carcinoma of no specific subtype, for tumor size, histologic grade, amount of stromal infilttration, vascular invasion, axillary lymph nodal metastases, and sinus histiocytosis in axillary lymph nodes. Staging by this system correlates well with survival in cases treated by radical mastectomy. The essential features to be studied in pathologic specimens of breast cancer are also indicated.