The long-term effects of central-nervous-system enterovirus infections were examined in a controlled follow-up study of 19 children 2 1/2 to eight years of age who had been hospitalized with documented enterovirus infection 17 to 67 months before evaluation. Assessment included medical history, physical and neurologic examination, psychologic testing, and speech and hearing evaluation. Three children (16 per cent) had definite neurologic impairment, five (26 per cent) had possible impairment, and 11 (58 per cent) were free of detectable abnormalities. Children whose illness occurred during the first year of life, when compared to controls, were found to have significantly smaller mean head circumference (50.6 vs. 51.6 cm, P less than 0.033), significantly lower mean I.Q. (97 vs 115, P less than 0.007), and depressed languange and speech skills. Children whose illness occurred after the first year of life were not different from their controls. Children whith central-nervous-system enterovirus infection may have neurologic impairment when infection occurs in the first year of life.