Few published human data are available concerning the acute toxicity of the new antiepileptic drug oxcarbazepine of which the metabolite 10-monohydroxy derivate (MHD) is the pharmacologically effective compound. Two hours after a documented overdosage of more than 100 tablets oxcarbazepine, the serum level of the parent compound was 10-fold higher than the therapeutic dosage (31.6 mg l -1 ). However, the concentration of MHD, which peaked 7 h after intake, was only twofold higher (59.0 mg l -1 ). No life-threatening situations occurred and the patient fully recovered. The fact that oxcarbazepine is a prodrug and that the formation of the active M HD metabolite is a rate-limiting process may contribute to the relative low toxicity of the drug in overdose.