ABSTRACT.Out of 109 children with infantile spasms (IS), prospectively tested during the years 1976 to 1979 in Denmark, 52 children were examined by cranial computed tomography (CT). The classification of IS into cryptogenic (CR), symptomatic (SY) and doubtful (DO) was done clinically without considering the CT‐findings. Sixty per cent of the scannings were abnormal. Only 6/30 (20%) of the children in ACTH treatment were found to develop cerebral atrophy which means that this finding is not an obligatory side‐effect of ACTH treatment of children with IS. Normal CT‐findings were found in 50% of the CR and 50% of the SY + DO‐groups, and could not be used as a prognostic tool for estimating the mental development. This was also the case for children with cerebral atrophy. Abnormal CT‐findings (minus atrophy) were highly correlated to the group with clinical symptoms and indicate an extremely unsatisfying long‐term mental prognosis. CT‐scanning is a valuable tool for the examination of clearing children with inf