A retrospective study was conducted to investigate the effects of CNS prophylaxis with 1,800 cGy cranial irradiation on standing height growth of children with acute lymphoblastic leukemia (ALL). Seventeen longterm survivors (DFS over 5 years ) of ALL and Non-Hodgkins Lymphoma who had been admitted at pediatric department of Inje University Seoul Paik Hospital from January 1982 to September 1988 were studied. The long term survivors were divided into two groups by prophylactic treatment modality; intrathecal chemotherapy alone (Group I, 7 cases), intrathecal chemotherapy with cranial irradiation (Group II, 10 cases). The heights of each groups were compared normal standard growth of the sane aged children by mean SD score (The SD score was calculated with the use of the following formula). SD score=(x-x)/SD (x; height measurement, x; mean height for age of the normal population SD; standard deviation). The results were as follows; 1) The mean SD scores of Group I and Group II at diagnosis were -0.30 and -0.17, which were smaller than height of normal child. 2) In Group 1, the mean SD scores after the end of treatment were -0.14 of 1 year, 0.03 at 2 years and 0.01 at 5 years, which suggests that were normal height velocity and catch-up growth in these patients (P<0.05). The height of 1 year after the beginning of treatment were particularly smaller than that of the normal children (P<0.05). 3) The mean SD scores 5 years after the end of treatment were 0.10 in Group I and -0.17 in Group II, which shows strong tendency to statistical difference among these two groups. If larger numbers of patients are evaluated, it, however, may turn significant. In conclusion, 1,800 cGy cranial irradiation in ALL children significantly affects on height growth. We recommend to evaluate growth hormone for patient with 1,800 cGy cranial irradiation and to treat them with growth hormone.