Antiepileptic drugs taken by pregnant epileptic women are known human teratogens. They may also cause pharmacological side effects in the newborn, i.e. sedation and or withdrawal symptoms. We examined the relationship between the maternal antiepileptic therapy, neonatal behaviour and later neurological functions in infancy. The study comprised 40 children exposed in utero to a single antiepileptic drug (phenobarbitone, phenytoin, valproic acid). Valproic-acid-exposed children were the highest compromised, except for apathy, which was most profound in phenobarbitone-exposed neonates. Valproic acid serum concentrations at birth correlated with the degree of neonatal hyper-excitability and neurological dysfunction when children were re-examined 6 years later. We suggest that valproic acid may not only cause malformations but also cerebral dysfunction immediate and long term.