Résumé : We systematically reviewed the files of 51 infants presenting with infantile spasms and hypsarrhythmia in order to study the initial treatment strategies and the long term outcome. 80% of the infants were classified as symptomatic. In the nine participating centres, different treatment protocols were used, but the large majority of the children received vigabatrin as first line treatment. Second line options included hormonal treatment, topiramate and valproate. The time to reach cessation of infantile spasms was significantly shorter in the cryptogenic group than in the symptomatic group (50% at 13 days versus 66 days respectively) and was irrespective of the treatment used. The late follow up data (>2 years) showed that 60% of the children had epilepsy and that 75% of the children had a delay in their psychomotor development. Again, outcome in the cryptogenic group was better than in the symptomatic group, but also in the cryptogenic group, 50% of the children had a clear developmental delay, even if spasms were controlled early in the course of the disease. Our retrospective study illustrates that not only the underlying brain dysfunction is the major determinant for later outcome in infantile spasms (symptomatic group) but also even a short period of infantile spasms can be responsible for later developmental delay (cryptogenic group).