BACKGROUND: Antiepileptic drugs (AEDs) may impair cognitive function in epileptic patients. Oxcarbazepine (OXC, Trileptal(R)) is a recently developed AED. The effect of oxcarbazepine (OXC, Trileptal(R)) monotherapy on cognitive func-tion was studied prospectively in patients with partial or generalized epilepsies. METHODS: A total of 22 patients were started on OXC monotherapy and 18 out of them completed a 1-year follow-up. Nine patients didn't have any previous history of anticonvulsant medications. OXC was administered 600 to 1,500 mg twice daily after 10 to 14 days of titra-tion period. We used neuropsycological assessments (verbal learning and memory, visual memory, digit span, Trail Making, and verbal fluency) and auditory event-related potentials (P300) for the evaluation of cognitive function before and 1 year after OXC treatment. RESULTS: Twelve patients became seizure free and 6 patients showed the reduction in monthly seizure frequency. The adverse effects of medication were mild weight gain, GI problems, dizziness, fatigue and headache etc., but they were transient. In particular one patient experienced a feeling of alertness and clear-headed-ness with continuation of the medication. Neuropsycological tests showed a significant improvement of performance in verbal learning, word recognition and Trail Making test of type A. P300 latencies were significantly shortened, but their amplitudes were not changed. CONCLUSIONS: Even though many variable factors such as the age at onset of epilepsy, etiology of epilepsy, seizure frequency, seizure type, epileptic process itself and dosage of antiepileptic drugs influence cognitive function of epileptic patients, OXC at least does not seem to be harmful or rather slightly beneficial for cogni-tive functions.