Thirty-two long-term survivors of childhood leukemia who were followed up at the University of Texas M. D. Anderson Hospital were evaluated with a battery of 17 neuropsychologic tests. These tests were selected to assess the development of cognitive skills and functions associated with brain impairment in children. Statistically significant differences were found between the group of children given CNS irradiation and the nonirradiated group on full-scale IQ and verbal IQ scores, mathematics skills, constructional skills, and memory for spatial material. Of particular interest was the absence of differences in language-based measures of verbal memory and the presence of group differences on measures of memory for spatial material. While the sample size was small, the findings delineate specific areas likely to be affected. These results indicate the need for caution when including cranial irradiation in CNS prophylaxis. When any CNS treatment is given, it seems appropriate that provisions be made for assessment and remediation of affected skills.