We evaluated brain stem P30, contralateral frontal N37, and the vertex-ipsilateral central P37, N50 somatosensory evoked potentials (SEPs) obtained in response to stimulation of the tibial nerve in 10 patients with idiopathic dystonia. Results were compared with those obtained in 10 healthy subjects matched for age and sex. The amplitude of the brain stem P30 potential and of the contralateral frontal N37 response in dystonic patients was not significantly different from that recorded in normal subjects. The vertex-ipsilateral central P37-N50 complex, which is thought to originate in the pre-rolandic cortex, was significantly enhanced in patients compared with the control group. These results suggest the enhancement of the vertex-ipsilateral central P37-N50 complex might reflect an abnormal response to somatosensory inputs of a precentral cortex which is excessively activated because of a disorder of the basal ganglia. Such inefficient sensory processing in motor areas might contribute to motor impairment in dystonia.