Children with infantile autism sometimes show hyperesthesia or hypoesthesia to touch, pain, and/or temperature. To clarify the pathophysiology, we examined short-latency somatosensory evoked potentials (S-SEPs), elicited by median nerve stimulation, in 24 children with infantile autism (17 males, seven females; age range 2y 2mo–9y; mean age 4y 2mo [SD 1y 7mo]). We also evaluated relationships between S-SEP findings and clinical manifestations. Of the 24 children, 10 showed abnormal S-SEPs as follows: prolonged peak latency of N20 (n=2), extended interpeak latency of P13/14–N20 (n=7), appearance of a giant SEP (n=1), and a more than twofold right hemispheric peak-to-peak amplitude predominance of N20–P25 (n=5). In addition, a peak-to-peak amplitude of N20–P25 elicited by left median nerve stimuli was significantly higher than that obtained with right median nerve stimuli, which indicated right hemispheric hyperactivity relative to the left (p=0.008). Infantile autism is frequently associated with somatosensory abnormalities and right hemispheric hyperactivity relative to the left, especially in the primary somatosensory area. This is believed to contribute to the pathophysiology of infantile autism, especially the idiopathic form.