Acute lymphoblastic leukemia is the most frequent malignancy inchildhood. Acute leukemia represent aclonal expansion and arrest at aspecific stage of normal myeloid or lymphoid hematopoiesis, itconstitutes 97%of all childhood leukemia, peak incidence between 2-5years of age,accounts for 25-30%of all childhood cancer. Advances in protocols and genetic typing helped in identificationof high risk groups and subsequent need of intensive chemotherapyprotocols with or without prophylactic cranial irradiation. The aim of therapy is usually directed towards induction of aclinical and hematological remission. And maintance remission bysystemic chemotherapy and to guard againstC.N.S.relaps by prophylacticC.N.S therapy. The aim of work is to analysis the short and long term toxicityresulting from cranial irradiation in comparison with patients in whomthis modality was omitted, in addition, analysis of C.N.S relapse rate andresponse to therapy and its impact on disease free as well as overallsurvival will be done.