Radiotherapy effectively prevents local recurrences, but on the other hand still over 80% of non irradiated women are free from local relapse 5 years after breast surgery aiming at radical removal of the primary tumor. So far, there are no indications that radiotherapy to the breast after breast conservation saves lives. The marginal monetary cost for prevention of one local recurrence is about $41,000. Thus, one clinically relevant question is if there is a group of women where the benefits of radiotherapy after breast conservation is outweighed by psychosocial and medical side-effects. Unfortunately, we still lack information from several areas, which makes a detailed cost-benefit analysis uncertain today. The problem situation would change: 1) If we knew more about the pathogenesis of local recurrences and thus also could undertake preventive measures other than radiotherapy. 2) If there was more information on risk factors for local recurrence, and we could identify a low-risk group that could be spared treatment. 3) If there were more valid empirical information on the psychosocial side-effects--both of a local recurrence and of the radiotherapy. 4) If the long-term--positive and negative--effects of radiotherapy were better quantified. Until we have new information, postoperative radiotherapy after breast conservation remains the standard.