Postoperative radiotherapy is controversial after radical mastectomy. Recent clinical trials have shown an increase in survival with this irradiation and conclusions of previous meta-analyses should be reconsidered. The results of a large number of randomized clinical trials in which women received post-mastectomy radiotherapy or not have been reviewed. These trials showed a decrease in locoregional failure with the use of postoperative radiotherapy but survival advantages have not been clearly identified. A larger number of randomized clinical trials compared postoperative radiotherapy alone, chemotherapy alone and the association of the two treatments. They showed that chemotherapy was less active locally than radiotherapy and that radiotherapy and chemotherapy significantly increased both disease-free and overall survival rates in the groups which received postoperative radiotherapy. These favourable results were, however, obtained with optimal radiotherapy techniques and a relative sparing of lung tissue and cardiac muscle. Many retrospective clinical analyses concluded that results obtained in locoregional failure rate were poor and that these failures led to an increase in future risks. Both radiotherapy and systemic treatment should be delivered after mastectomy, reserved for patients with a high risk of locoregional relapses, particularly of nodes and/or tumors with a diameter > or = 5 cm. However, radiotherapy could produce secondary effects, and techniques of radiotherapy should be optimal.