The risk of an adverse outcome to pregnancy is increased in women with epilepsy. This is partly attributable to antiepileptic drugs. Guidelines for the management of pregnancy in women with epilepsy generally advise against polytherapy but make no distinction between the risks of different drugs. Several recent studies have however shown greater risk of adverse outcome in offspring exposed to sodium valproate in utero, particularly at higher doses. The outcome of pregnancy was monitored to identify antiepileptic drug treatment associated with a poor outcome in a mainly prospective study of women attending an outpatient clinic. From January 1990 to December 1999 all 69 pregnancies in women referred to the clinic were monitored. Drug treatments and other risk factors were recorded. In each child dysmorphic features, developmental delay and structural anomalies were assessed and graded. Data were analysed for drug- and dosage-dependent differences in outcome. In each assessment area a positive association between adverse outcome and dose was found for sodium valproate but not for carbamazepine. Severe adverse outcomes were found only in children exposed to sodium valproate at maternal doses above 1000 mg per day.