Prolonged antiepilepsy drug treatment can result in secondary carnitine deficiency. The effect of oxcarbazepine on carnitine metabolism has not been reported previously. In this study, serum concentrations of total and free carnitine were measured in 20 children with epilepsy treated with oxcarbazepine monotherapy and were compared with 20 children with epilepsy who were taking carbamazepine as monotherapy. The assays were performed between 3 and 6 months of anticonvulsant treatment. The mean values of serum total and free carnitine levels in patients receiving carbamazepine monotherapy were 63.0 +/- 20.7 mumol/L and 49.1 +/- 16.7 mumol/L, respectively. The mean values of serum total and free carnitine levels in patients receiving oxcarbazepine monotherapy were 64.2 +/- 17.4 mumol/L and 50.3 +/- 13.7 mumol/L, respectively. The values were all between normal ranges. No significant difference was observed in the level of total and free carnitine levels between the two groups. Our results suggest that neither oxcarbazepine nor carbamazepine as monotherapy causes carnitine deficiency in otherwise healthy children with primary idiopathic epilepsy.