Behavioral measurement of brain function was conducted in 40 children, one or more years after their recovery of Reye syndrome. Test measures included standard indices of intelligence, school achievement, visual-motor coordination and social maturity, plus the Halstead-Reitan Neuropsychological Batteries. There was a strong correlation between the degree of impaired neuropsychologic function and clinical grade at admission, the duration of impaired consciousness, and the number of exchange transfusions required. Patients with milder disease had normal brain function and fewer school problems. Language and perceptual-motor performance significantly improved with increasing years in recovery, suggesting that some of the disturbances of brain functioning are transient. The statistical analysis indicated that there are lasting, often subtle disturbances of higher cognitive function as a result of Reye syndrome. These deficits, not always apparent on clinical examination, are clearly correlated with the extent of neurologic involvement. This quantitative assessment of neuropsychologic function is a basis for determining the "quality of survival" in Reye syndrome, and such measurements should be included in the comparative evaluation of Reye syndrome treatment programs.