Radiation dose-effect relationship is reviewed. In conservative treatment of early breast cancer, necessity of radiation is discussed and surgery with radiotherapy technique in our hospital is presented. Our procedures consist of lumpectomy which is removal of 1 cm of normal tissue containing primary breast cancer and complete axillary dissection and postoperative radiotherapy of 46 Gy with 9 Gy of electron boost. Since November 1987, 51 patients treated by this procedure have shown a good local control and a satisfactory cosmetic results. We can conclude that the positive aspects of radiotherapy in the management of conservative therapy for early breast cancer are overwhelming.