AbstractData on incidence, etiology, therapy and prognosis of infantile spasms are reviewed. Infants with infantile spasms have a lower CSF GABA concentration than other epileptics. In a large proportion of cases the etiological factors of infantile spasms can now be elucidated with some certainty. Especially, the new neuroradiological and virological methods have enabled a more accurate diagnosis. There have been changes in the etiological pattern over the years. The optimal dosage and duration of ACTH or glucocorticoid therapy have not been established. In the Finnish study the large ACTH doses (120–160 IE) generally used in many Nordic European countries did not carry a better prognosis than the smaller doses (20–40 IE). Therapeutic response showed no correlation with the Cortisol secretion rate but the infants who responded well had a high dehydroepiandrosterone‐androstenedione concentration ratio. Side‐effects of ACTH therapy are relatively common and more common with large doses than with smaller ones. The most common side‐effects are infections and arterial hypertension. There were disturbances of calcium and phosphate metabolism during ACTH therapy. Severe nephrocalcinosis was seen in some infants at autopsy. Fluid disturbances were common at termination of ACTH therapy. ACTH therapy causes adrenal hyporesponsiveness. The therapy should be modified to improve the