Objective: To delineate the risk to child IQ associated with frequently prescribed antiepileptic drugs.Methods: Children born to women with epilepsy (n 5 243) and women without epilepsy (n 5 287) were recruited during pregnancy and followed prospectively. Of these, 408 were blindly assessed at 6 years of age. Maternal and child demographics were collected and entered into statistical models.Results: The adjusted mean IQ was 9.7 points lower (95% confidence interval [CI] 24.9 to 214.6; p , 0.001) for children exposed to high-dose (.800 mg daily) valproate, with a similar significant effect observed for the verbal, nonverbal, and spatial subscales. Children exposed to high-dose valproate had an 8-fold increased need of educational intervention relative to control children (adjusted relative risk, 95% CI 8.0, 2.5-19.7; p , 0.001). Valproate at doses ,800 mg daily was not associated with reduced IQ, but was associated with impaired verbal abilities (25.6, 95% CI 211.1 to 20.1; p 5 0.04) and a 6-fold increase in educational intervention (95% CI 1.4-18.0; p 5 0.01). In utero exposure to carbamazepine or lamotrigine did not have a significant effect on IQ, but carbamazepine was associated with reduced verbal abilities (24.2, 95% CI 20.6 to 27.8; p 5 0.02) and increased frequency of IQ ,85.Conclusions: Consistent with data from younger cohorts, school-aged children exposed to valproate at maternal doses more than 800 mg daily continue to experience significantly poorer cognitive development than control children or children exposed to lamotrigine and carbamazepine. Antiepileptic drugs (AEDs) are associated with teratogenic risk to the development of the fetus, with the prevalence of major congenital malformations differing by treatment type and dose. Determining the association between exposure to AEDs and child cognitive functioning represents a challenge, and a number of different methodologies have been utilized in its investigation including case studies, 2-4 retrospective studies, 5,6 and prospective studies. 7-15 Despite limitations, 16 there is growing evidence that exposure to sodium valproate (VPA) in utero is associated with significantly poorer functioning. [10][11][12]15,17 Prospective studies consistently document that VPA is associated with an increase in risk of cognitive impairment in young children, 10,12,15 but any longer-term effects are unlikely to be comprehensively documented until the children studied are of school age, when cognitive development is more stable.10 In a comparison across AED monotherapies, a significantly poorer IQ in school-aged children exposed in utero to