We present the first assessment of motion vision in childhood autism. Postural reactivity to visually perceived motion was measured in five autistic children and 12 normal controls of the same chronological age. Anteroposterior as well as total body sway occurring on a force platform in response to movements in the visual environment were compared. Autistic children were posturally more unstable than normal children and quite insensitive to visually perceived environmental motion. Some implications of this impairment for sensorimotor and social communication development in infantile autism are discussed.