Managing epilepsy during pregnancy is to balance the maternal and fetal risks associated with uncontrolled seizures against the potential teratogenic effects of antiepileptic drugs (AEDs). A rational approach requires knowledge of such risks as well as an understanding of the effects of pregnancy on seizure control and of gestational effects on AED disposition. Uncontrolled tonic-clonic seizures are potentially hazardous to the mother and, although strict evidence is lacking, are generally also assumed to be more harmful to the fetus than are AEDs. However, infants who have been exposed to AEDs in utero run an increased risk of congenital malformations: approximately twice the rate reported in the general population. Earlier literature has largely failed to demonstrate differences in birth defect rates with different treatment regimens, which can be ascribed mainly to insufficient sample sizes. More recent data have indicated higher malformation rates with exposure to valproic acid compared with some other major AEDs. The teratogenic effects of valproic acid appear to be dose dependent, with higher risks at dosage levels >1000 mg/day. Polytherapy involving treatment with more than one AED also seems to be associated with an increased risk of birth defects compared with monotherapy. Recently, a few small-scale studies have investigated the possibility that exposure to AEDs in utero may adversely affect the postnatal cognitive development of the offspring. Some of these studies have suggested that valproic acid poses a higher risk compared with other AEDs in this respect. These signals are important, but must be interpreted with caution because of the methodological shortcomings of the studies and because adequately powered prospective studies are necessary to draw firm conclusions. More reassuring findings have emerged regarding the obstetric outcome of pregnancy and the risk of worsening of epilepsy during pregnancy. In particular, it seems that the risk of obstetric complications is not significantly increased. Furthermore, most of the women with epilepsy have no change in their seizure frequency during pregnancy. The disposition of many AEDs may change during pregnancy, reflected in declining plasma drug concentrations. This seems to be most pronounced for lamotrigine and possibly also for oxcarbazepine, and can result in break-through seizures. The common treatment strategy has been to use the appropriate AED for the woman's seizure disorder as monotherapy in the lowest effective dosage throughout pregnancy, the objective being to use AEDs in such a way that generalised tonic-clonic seizures are avoided but with minimised risks to the fetus, the newborn and the breast-fed infant. Valproic acid should be avoided if possible. Any major change in the treatment of a woman with epilepsy should ideally be completed before conception. Regular monitoring of drug concentrations is recommended during pregnancy, in particular for lamotrigine and oxcarbazepine.