Radiation techniques and indications in leukemias have been described in detail, yet prophylactic cranial irradiation in acute leukemia still has few indications. Cerebrospinal and testicular irradiation are reserved for relapsing disease. Radiation usually results in rapid functional improvement when used in neurologic emergencies and symptomatic neurologic or gross tumors relapses. Nevertheless, the improvements recently obtained by systemic chemotherapy have resulted in the reduction in the use of irradiation, especially in children, where it was considered deleterious with neuropsychological sequellae. Splenic irradiation remains useful for symptomatic myeloproliferative syndrome.