Background: The present paper is an update of the practical guidelines for radiotherapy of breast cancer published in 2006 by the breast cancer expert panel of the German Society of Radiation Oncology (DEGRO) . These recommendations have been elaborated on the basis of the S3 guidelines of the German Cancer Society that were revised in March 2007 by an interdisciplinary panel . Methods: The DEGRO expert panel performed a comprehensive survey of the literature, comprising lately published meta-analyses, data from recent randomized trials and guidelines of international breast cancer societies, referring to the criteria of evidence- based medicine . In addition to the more general statements of the German Cancer Society, this paper emphasizes specific radiotherapeutic aspects. It is focused on radiotherapy after breast-conserving surgery. Technique, targeting, and dose are described in detail. Results: Postoperative radiotherapy significantly reduces rates of local recurrence. The more pronounced the achieved reduction is, the more substantially it translates into improved survival. Four prevented local recurrences result in one avoided breast cancer death. This effect is independent of age. An additional boost provides a further absolute risk reduction for local recurrence irrespective of age. Women > 50 years have a hazard ratio of 0.59 in favor of the boost. For DCIS, local recurrence was 2.4% per patient year even in a subgroup with favorable prognostic factors leading to premature closure of the respective study due to ethical reasons. For partial-breast irradiation as a sole method of radiotherapy, results are not yet mature enough to allow definite conclusions. Conclusion: After breast-conserving surgery, whole-breast irradiation remains the gold standard of treatment. The indication for boost irradiation should no longer be restricted to women ≤ 50 years. Partial-breast irradiation is still an experimental treatment and therefore discouraged outside controlled clinical trials. Omission of radiotherapy after breast-conserving surgery of DCIS should be restricted to individual exceptions.