A long-term open multicenter trial was carried out in 15 European centers with therapy-resistant epileptics to evaluate the efficacy and safety of progabide, a new antiepileptic GABA receptor agonist; 187 patients, suffering from partial epilepsy (57%), primary generalized epilepsy (20%), secondary generalized epilepsy (21 %), and unclassified generalized epilepsy (2 %), participated in the study. All patients had a total seizure frequency higher than one per month in spite of standard antiepileptic medication; 46 % had a mean partial seizure frequency from daily to weekly. Progabide was administered at a mean daily dose of 30.5 mg/kg/day as an add-on to the standard antiepileptic drugs up to one year in 115 patients; 37 patients (19.8%) dropped out because of reasons which were not drug-related (bad compliance, lost to follow-up); in 12 patients (6.5%) progabide was withdrawn for side effects and in 20 (10.7%) for lack of efficacy. 71.3% of patients treated for one year (62% considering the ‘cumulative’ number of patients) experienced more than a 50% reduction in seizure frequency. This reduction was equally present in patients with partial epilepsy (63.9%) and with generalized epilepsy (62.2% of patients with primary and 57.1% with secondary generalized epilepsy). No signs of tolerance phenomena to the antiepileptic effect of progabide were observed. No side effects were reported in 56.7% of the patients. Clinical side effects were mild and transient, leading to progabide discontinuation in 6.5% of the patients only; an increase in SGPT was observed in 5.7% of the patients, these increases were transient and without any clinical symptom. The results of this long-term study confirm the results from several open and controlled trials and show that progabide is a valuable antiepileptic also in long-term ther