Several meta-analyses of the effects of radiotherapy in breast cancer were published. Methodological quality varied largely in these studies, from simply gathering data from published studies or even published abstracts, to more rigorous studies gathering individual data from each patient having participated in the trials analysed. A model of the latter is represented by the successive meta-analyses from the Early Breast Cancer Trialists' Cooperative Group (EBCTCG). These studies have had a strong impact on the clinical practice of radiotherapy in breast cancer, by demonstrating its long-term potential toxic effects, but also its ability to decrease the long-term breast-cancer mortality, regardless of the effects of other breast-cancer treatments. Therefore, it has contributed to the continuous improvement in the techniques of radiotherapy, as well as to its use in the multidisciplinary management of breast-cancer patients.