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1. The long term safety and efficacy of vigabatrin has been studied in 254 patients with refractory epilepsy (82% with partial seizures) in 23 different clinics in eight European countries. 2. This was an open multicentre study in which patients who had experienced a significant benefit from vigabatrin and had continued to take the drug for 1 year or longer were eligible for evaluation. The mean duration of therapy in the 254 patients was 22.7 months; 72 patients received vigabatrin for more than 2 years. 3. Patients were severely affected by epilepsy with a median monthly seizure frequency of 15.7 despite taking an average of 2.2 antiepileptic drugs. On vigabatrin, the median seizure frequency was about 35% of baseline, remaining stable over time despite a 10% reduction in the number of concurrent medications. 4. The lack of tachyphylaxis to the antiepileptic effect of vigabatrin is shown by the small number of patients who discontinued for insufficient efficacy (11%), two thirds of them during the first 6 months of follow-up. Maintenance of efficacy is also clearly demonstrated by analysis of 2 year and 3 year cohorts of patients. 5. Clinical and biological tolerability was excellent. There was a very low rate of drop out for adverse events (1.6%). Adverse events, mainly sedation, irritation and weight gain were mostly mild and transient. 75% of patients reported no adverse event at all. 6. Safety evaluation included serial neurological, ophthalmological and general examinations: no new abnormal clinical feature or adverse event emerged with long term therapy.