Neoadjuvant chemotherapy can be used before radiotherapy to combat microscopic metastatic loci and to facilitate irradiation. Improvement in the survival time by impeding the dissemination of metastases seems to be real for breast cancer, but has not been observed to date in randomized studies of ENT cancers. Neoadjuvant chemotherapy in Hodgkin's disease has improved survival time and tolerance to irradiation, allowing a lowering of the total doses used and the volumes irradiated. In breast and ENT cancers, it has become possible, due to tumor regression, to replace mutilating treatments with more conservative ones consisting of radiotherapy alone, without increasing the risk of local relapse. Indeed, it is in this domain that neoadjuvant chemotherapy is the most useful. Two important conditions must be met for its successful application: a) a sufficiently effective regimen must be chosen, in order to prevent tumor growth prior to irradiation (which would aggravate the prognosis); and b) an accurate identification and localization of the tumor before undertaking any treatment so as to not detract from the effectiveness of the radiotherapy.