Altogether 235 patients with newly diagnosed epilepsy were randomly allocated to treatment with either oxcarbazepine (OXC) or carbamazepine (CBZ) in a double-blind multicentre trial. After a titration phase of 4-8 weeks the optimum individual dose of trial medication was determined and treatment with this dose was continued for another 48 weeks.The results of the study indicate that there is no significant difference in seizure frequency between OXC and CBZ; no correlation was found between the therapeutic effect and EEG in either treatment group. OXC caused significantly (p = 0.04) fewer "severe" side-effects than CBZ. Global evaluation of tolerability showed a trend towards better tolerability of OXC. There way no correlation between either efficacy or tolerability and serum trough levels of the investigational drugs. Clinically relevant abnormal laboratory test findings were observed in two patients, both on CBZ.In conclusion, OXC is a major anti-epileptic drug, which is as effective as CBZ in the treatment of partial seizures and generalized convulsions. With fewer side-effects than CBZ, it represents a valuable alternative particularly in patients who develop side-effects which prevent optimum seizure control.