Cognitive function and school achievement were studied prospectively over 3 to 4 years in 19 children treated for brain tumors with whole-brain radiotherapy; 14 of 19 also received adjuvant chemotherapy. For the group as a whole, mean IQ fell from a baseline of 104 to 92 at follow-up (p < 0.01). Age was inversely correlated with change in IQ over time (r = 0.71; p < 0.001). Children younger than 7 years at diagnosis had a mean IQ loss of 27 points, while children over 7 years at diagnosis showed no significant decrease in IQ. Decline in IQ occurred between baseline and year 2 of follow-up; none could be documented between years 2 and 4. All children younger than 7 years at diagnosis were receiving special education at follow-up; 50% of the children over 7 years at diagnosis were receiving supplemental educational services.