[en] Intellectual impairment in pediatric acute lymphoblastic leukemia (ALL) is thought to be caused by the effect of treatment on the central nervous system. We therefore assessed the characteristics and tendencies of patients' cognitive ability by using the K-ABC (Kaufman Assessment Battery for Children), an intelligence test. The subjects were 28 patients treated for ALL (males 18, females 10, age 4.7-12.0 years). The patients who took the K-ABC test were divided into irradiation group (15 patients who received brain irradiation as prophylactic treatment) and a non-irradiation group (13 patients whose brain was not irradiated), and evaluated the results. The K-ABC consists of a cognition processing scale and an acquisition level, and the cognition processing scale consists of a sequential processing scale and simultaneous processing scale. Patients were assessed in regard to various factors: 1. sex, 2. age of onset, 3. length of hospital stay, 4. age at the time of irradiation, 5. radiation dose, 6. score on the cognition processing scale, and multiple comparisons were made based on analysis of variance, least significant differences (1, 2, 3, 6), and the t-test (4, 5). Sequential processing ability was impaired in the patients with impaired cognitive processing in both groups. Part of simultaneous processing ability (ability to understand spatial relationships) tended to be reduced in the irradiation group in addition to the impairment in sequential processing ability, and factors 1 and 4 influenced cognitive ability in the irradiation group. The ability of girls decreased more than in boys. When children were irradiated below 4 years of age, their ability decreased even more. Regardless of whether they had received radiation therapy, all of the patients had received chemotherapy, including methotrexate, etc., and the anticancer drugs may have reduced their cognitive ability. The reduction of simultaneous processing ability may have been caused by the addition of irradiation. A method of applying the cognitive characteristics observed in this study to support childhood patients with intellectual impairment needs to be designed. (K.H.)