OBJECTIVE: We report the results of a prospective study of the efficacy and tolerability of levetiracetam, a new antiepileptic drug with a unique mechanism of action, in comparison with controlled-release carbamazepine as first treatment in newly diagnosed epilepsy. METHODS: Adults with > or =2 partial or generalized tonic-clonic seizures in the previous year were randomly assigned to levetiracetam (500 mg twice daily, n = 288) or controlled-release carbamazepine (200 mg twice daily, n = 291) in a multicenter, double-blind, noninferiority, parallel-group trial. If a seizure occurred within 26 weeks of stabilization, dosage was increased incrementally to a maximum of levetiracetam 1,500 mg twice daily or carbamazepine 600 mg twice daily. Patients achieving the primary endpoint (6-month seizure freedom) continued on treatment for a further 6-month maintenance period. RESULTS: At per-protocol analysis, 73.0% (56.6%) of patients randomized to levetiracetam and 72.8% (58.5%) receiving controlled-release carbamazepine were seizure free at the last evaluated dose (adjusted absolute difference 0.2%, 95% CI -7.8% to 8.2%) for > or =6 months (1 year). Of all patients achieving 6-month (1-year) remission, 80.1% (86.0%) in the levetiracetam group and 85.4% (89.3%) in the carbamazepine group did so at the lowest dose level. Withdrawal rates for adverse events were 14.4% with levetiracetam and 19.2% with carbamazepine. CONCLUSIONS: Levetiracetam and controlled-release carbamazepine produced equivalent seizure freedom rates in newly diagnosed epilepsy at optimal dosing in a setting mimicking clinical practice. This trial has confirmed in a randomized, double-blind setting previously uncontrolled observations that most people with epilepsy will respond to their first-ever antiepileptic drug at low dosage.