Infantile spasms are rare. They typically begin during the first year of life, usually starting around three to seven months of age.

Infantile spasms consist of clusters of sudden, quick movements. Typically, if the child is sitting up, the head may fall forward, the arms will flex forward, and the body may flex at the waist. If lying down, the knees will be drawn up with arms and head flexed forward as if the body is reaching for support.

Individual spasms last only one or two seconds. They often repeat in a series of five to 50 or more. A child may have many series per day. Spasms are most likely to occur when the child is drowsy, just waking from a nap or falling asleep.

Infantile spasms may occur as part of West syndrome. They sometimes resist anticonvulsant medication.