BACKGROUND AND PURPOSE: Pregabalin has demonstrated efficacy in controlled trials as adjunctive treatment in patients with refractory seizures. METHODS: This open-label, 21-week study in adults with at least two partial seizures in the last 2 months, who were inadequately controlled with one to three antiepileptic drugs, evaluated pregabalin 150-600 mg/day (dosed twice daily). The study comprised a prospective or retrospective 8-week baseline phase, and 9-week dose optimization and 12-week maintenance periods. The primary assessment was the mean percentage change in 28-day seizure frequency between baseline and end-point (last 12 weeks of treatment, last observation carried forward, modified intention-to-treat population). RESULTS: Four hundred and seventy-six patients from Europe were included in this study (51% men; mean age/epilepsy duration 40.1/24.1 years). The median baseline seizure frequency was 5.5/28 days. Amongst the patient population, 78% completed the 21-week treatment period; 7% discontinued for lack of efficacy and 12% because of adverse events (AEs). The mean last pregabalin dose was 359 mg/day. The mean (95% CI) reduction in seizure frequency was 36% (31%; 41%). The median reduction was 33%, and 39% of patients had a >or=50% reduction in seizure frequency. There were 19% and 8% of patients free of seizures during their last 4 and 12 weeks of treatment, respectively. The three most common AEs were dizziness (17%), somnolence (13%) and weight increase (13%). CONCLUSIONS: This open-label study of pregabalin demonstrated efficacy that was consistent with that observed in previous controlled epilepsy trials. Pregabalin was well tolerated. The AE profile was also consistent with that reported in previous trials.