Previous studies have shown that magnetic resonance imaging (MRI) is sensitive to white matter changes in children receiving cranial radiation of 3000 cGy or greater. The current study used MRI to investigate the integrity of white matter in children receiving 1800 to 2400 cGy of cranial radiation. Ten survivors of acute lymphoblastic leukemia (ALL) who received intrathecal methotrexate (MTX) and either 1800 or 2400 cGy of cranial radiation were studied with MRI and neuropsychologic testing. Magnetic resonance (MR) scans were normal in nine of ten patients. One patient had prominent and asymmetrical lateral ventricles and mildly enlarged cortical sulci. White matter tracts were normal in appearance. However, seven of nine children had below average intellectual functioning. Results indicate that children receiving less than 2500 cGy of cranial radiation fail to show white matter changes on MRI, despite evidence of cognitive impairment.