Therapeutic drug monitoring of antiepileptic drugs. While plasma levels of commonly used antiepileptic drugs (AEDs) are currently used to support drug dosing, this strategy is based on few systematic data. While in adult patients plasma level monitoring may be useful to establish the diagnosis of drug resistance, in children drug levels have no place in determining the management of epilepsy. In contrast, an estimation of AED plasma levels may be important for drug optimization in the various specific situations that are encountered in clinical practice. Most important is the use of plasma levels in the estimation of the pharmacokinetics of drug-drug interactions with other anticonvulsant medications or non-antiepileptic drugs. However, a significant correlation between plasma levels and clinical effectiveness remains to be documented for many of these drugs. Because the evidence in favor of plasma level monitoring is weak, we feel that plasma levels of antiepileptic drugs cannot yet be recommended for routine use in clinical practice. This manuscript reviews the pharmacokinetic parameters of AEDs in children and critically reviews available data on the clinical relevance of plasma levels in children with epilepsy. The available data indicate that plasma levels can help define the clinical relevance of non-therapeutic AED levels and that they are helpful in monitoring drug interactions. They can also be useful in the case of adverse drug reactions and to guide dosage regimen adjustment. The limitations of the approach are discussed and alternative or complementary approaches are suggested.