TBI is currently used as a conditioning regimen in bone marrow transplantation (BMT) with various Radiation doses, fractionation scheduling and dose rate. In children, the most frequent neoplasms treated with TBI are leukemias and advanced Neuroblastoma (NB). In leukemias the radiation dose plays an important role, particularly in patients at high risk of relapse. In NB the inclusion of TBI in pretransplant therapy does not seem to produce any difference in survival. In pediatric patients TBI involved particular problems of technique dosimetry and toxicity.