Breast carcinoma is the most frequent form of cancer in women. In Switzerland 1265 women died of it in 1975, the mortality rate is rising slowly, the cause of this being unclear. There is no uniformity about the best treatment of breast cancer. We analyzed 454 carcinomas, operated in the years 1961--1971 according to Halsted, Patey and McWhirter. We found similar 5- and 10-year survival rates with the Halsted and the Patey method of operation, however, decidedly worse results with the simple mastectomy. Today we recommend the modified radical excision of the breast after Patey at all stages; in addition we treat all patients with postoperative X-ray therapy or prescribe an adjuvant cytostatic therapy based on the experimental study of the SAKK (Swis Therapy Group for Clincal Cancer Research).