The locoregional control is a crucial step in the achievement of a cancer cure. After mastectomy, the locoregional irradiation clearly reduces the chest wall and nodal relapses, especially with initial lesions more than 5 cm or with nodal involvement and/or large lymphatic or vascular emboli. Two recent randomized trials confirmed the benefit of well-adapted locoregional irradiation. In the Danish trial, including premenopausal "high-risk" women treated by mastectomy and chemotherapy (CMF protocol), the radiotherapy reduced the locoregional relapses from 32 to 9% (P < 0.001) and increased the 10-year survival rates from 45 to 54% (P < 0.001). These results are now also confirmed in a postmenopausal group, with an increased 10-year survival rate of 36 to 45% (P < 0.001). In the Canadian trial, locoregional relapse rate decreased from 25 to 13% and 10-year survival rate increased from 56 to 65%. The meta-analysis published in 1995 by the Early Breast Cancer Trialist Collaborative Group (EBCTCG) showed only a modest benefit due to locoregional irradiation in breast cancer. However, when small trials and older trials started before 1970 are excluded due to imperfect methodologies and for inadequate irradiation techniques, the benefit of the "modern" radiotherapy appears significant in the 7,840 patients selected in this way. Thus, since the locoregional irradiation can avoid some metastatic evolutions developed only after "local" or "nodal" relapse, it must be integrated in a multidisciplinary strategy. Nevertheless, this treatment must be safe and this is possible by the use of new techniques, including the definition of anatomical volumes and previsional dosimetry. The most important point concerns the treatment of the internal mammary nodes, especially when previous chemotherapy including anthracyclines was performed. The use of a direct field, with at least 40% of the dose delivered by electrons in an alternating scheme, is recommended to ensure very good protection of the heart and lungs.