 Study AML-BFM 98 has already focussed on the question of whether or not doses of CNS irradiation of 12 Gy and 18 Gy are equivalent with regard to their capacity of reducing the risk of relapse. As the results of study AML-BFM 87 confirmed the necessity of CNS irradiation, but did not reveal the necessary minimum dose, this randomisation has been implemented in order to prevent, as far as possible, late sequelae of CNS irradiation by reducing the radiation dose objective three. 