We report an assessment of the intellectual functioning after one year of therapy of 117 children treated for acute lymphoblastic leukemia (ALL) who were assigned to one of four protocols for central nervous systems (CNS) prophylaxis. These protocals were (a) 2400 rad cranial irradiation plus concurrent intrathecal methotrexate (i.t. MTX), (b)i.t. MTX alone, (c) 1800 rad cranial irradiation plus concurrent i.t. MTX, and (d) a protocol for high-risk patients that included intensive systemic chemotherapy plus 2400 rad delayed irradiation. Neuropsychological evaluation consisted of the Wechsler intelligence scales, the Wide Range Achievement Test, and selected tests from the Halstead-Reitan Neuropsychological Battery administered one year after diagnosis. All patients performed in the average range on measures, although the high-risk patients performed marginally worse than did the others. In general, our results do not support previous reports that cranial irradiation results in early adverse neuropsychological sequelae.