Somatosensory evoked potentials (SSEPs) were investigated to evaluate the function of the central nervous system in 53 severely handicapped patients. P9-P13 interpeak latencies of these patients were within normal limits in comparison with those of normal controls. But P13-N20 interpeak latencies showed various abnormalities including prolongation or absence. On etiological study, prenatal onset cases, especially in migration disorders, had markedly prolonged P13-N20 and postnatal onset cases frequently showed the absence of N20. Most of the patients showing diffuse brain destruction on CT scan revealed the absence of N20.