45 children with ALL treated with intrathecal Methotrexate and radiation therapy, all in hematologic remission, have been examined with brain CT at intervals varying from 3 to 6 years after completion of CNS prophylaxis. Abnormalities were detected in 20% of the children; the main findings were: calcifications within the brain parenchyma in 3 patients; enlargement of the ventricular system and/or sulci in 8. The 3 patients with calcifications had seizures during or after treatment whereas those with dilatation of the ventricular system or sulci presented no neurological signs.