Data on incidence, aetiology, therapy and prognosis of infantile spasms are reviewed. In a large proportion of cases the aetiological factors of infantile spasms can now be established with some certainty. Especially the new neuroradiological and virological investigative methods have enabled a more accurate diagnosis. There have been changes in the aetiologic pattern over the years. The optimal dosage and duration of ACTH or glucocorticoid therapy have not yet been established. In the Finnish study the large ACTH doses (120-160 IE) generally used in many Nordic countries did not carry a better prognosis than the smaller doses (20-40 IE). Side-effects of ACTH therapy are relatively common. They are more frequent with large doses than with smaller ones. Measures can be taken to prevent or treat part of them. The prognosis and related factors in infantile spasms as well as some recommendations to improve them are reviewed.