METHODS To record prospectively combined motor- and somatosensory-evoked potentials in children during scoliosis surgery using Cotrel-Dubousset instrumentation, without using special anesthetic or muscle relaxant regimens. OBJECTIVE To determine the outcome of scoliosis surgery guided by a new technique of monitoring motor- and somatosensory-evoked potentials simultaneously. BACKGROUND Other techniques used to assess cord function generally are limited by special anesthetic requirements or assess only a limited part of the cord or monitor motor function separately from somatosensory function. METHODS Spinal cord function was monitored using epidural leads to record simultaneously the descending motor volley (by transcranial electrical stimulation) and the ascending somatosensory volley (by tibial nerve stimulation) at two spinal levels. RESULTS Combined motor- and sensory-evoked potentials were recorded successfully in 138 of 160 children (81%). Changes in evoked potential waveforms were seen in eight patients (5%), but resolved or lessened in response to appropriate measures. Curve correction was satisfactory, and there were no new postoperative deficits or worsening of preexisting deficits in any patient. CONCLUSIONS A spinal cord monitoring system is described that is safe, reliable, accurate, and makes it unnecessary to resort to the "wake-up" test.