[en] For preventing CNS leukemia in children with ALL, simple whole skull irradiation that included only retro-orbital spaces and not anterior part of the cribriform plate and first two cervical vertebrae had been given until March 1982 to patients who had remission after drug therapy. Since March 1982, however, such patients have received new modified cranial irradiation of Pinkel's method of preventive CNS therapy to include the cribriform plate. Pinkel's method usually includes first two cervical vertebrae in radiation port, but sometimes his method of radiation fails to reach the brain and the meninges on the anterior parts of the lamina cribrosa. In this study, a comparison of CNS-relapes ratio between these two methods of preventive CNS therapy was carried out. The frequency of CNS leukemia was remarkably high in patients given the simple whole skull irradiation. Of 18 patients, 7 developed CNS leukemia. Among these 7, 5 patients (71 %) had occurence of CNS-relapse within 1 year 7 months with the other one patient, making a total of 86 %, having CNS-relapse within 1 year 11 months. On the other hand, 17 of 39 patients who received new modified cranial irradiation were followed up for more than 1 year 9 months, and all patient had no CNS-relapse to date. This result showed that the irradiation of whole circulation areas of cerebrospinal fluid of the brain and the spine at first two cervical vertebra levels had great importance in preventing CNS-relapse after achievement of drug-induced remission. (author)