The cessation of infantile spasms and the disappearance of hypsarrhythmia in sleep EEG are the criteria for successful treatment in West syndrome. In a prospective study at the Children's University Hospital, 28 children with West syndrome (17 symptomatic, 7 cryptogenic, 4 idiopathic) were treated with vigabatrin monotherapy for at least 2 weeks. Seven children received vigabatrin 150 mg/kg/day, and 21 children received 65-75 mg/kg/day. Patients were classified as responders, when infantile spasms and hypsarrhythmia in sleep EEG disappeared within 2 weeks. After 2 weeks, 18 patients were seizure-free, 14 without hypsarrhythmia. Fourteen children were responders (8 symptomatic, 3 cryptogenic, 3 idiopathic), and 14 non-responders. The follow-up encompassed 6 months to 5.3 years (mean 20.3 months). In the responder group, 12/14 patients (6 symptomatic, 3 cryptogenic and 3 idopathic) remained seizure-free, no relapse of West syndrome occurred. In the non-responder group, ACTH was efficient in 11, valproic acid in 2 children and clonazepam in 1 child. Relapse occurred in 4 children after discontinuation of ACTH. At last visit EEG was normal in 8/14 responders and 1/14 non-responders. The efficacy of vigabatrin monotherapy was comparable to ACTH and occurred within 2 weeks.