Primary carcinoma of breast was treated in 967 patients from 1962 through 1972. Thirty-five of these patients had a second primary tumor of which 50% were discovered simultaneously. A family history for cancer was recorded in 26% of the patients with bilateral cancer. Patients found their tumor more often than the physician except in the simultaneous cases where the physician was more successful. Pathological examination showed 10% of the tumors were comedo, lobular carcinoma in situ, papillary, or tubular cancers. In the metachronous group, 50% of the axillae were involved on both sides. In the simultaneous cases the axilla was less frequently involved. Mammography, biopsies of the second breast, and prophylactic mastectomy in certain high-risk patients should improve survival rates.