Continuous intraoperative monitoring of spinal cord function using somatosensory evoked potentials (SSEP) has gained nearly universal acceptance as a reliable and sensitive method for detecting and possibly preventing neurologic injury during surgical correction of spinal deformities. In several reports, spinal cord injury was identified successfully based on changes in SSEP response characteristics, specifically amplitude and latency. Less well documented and used, however, is monitoring of peripheral nerve function with SSEPs to identify and prevent the neurologic sequelae of prolonged prone positioning on a spinal frame. The authors describe a patient who underwent surgical removal of spinal instrumentation but was not monitored. A brachial plexopathy developed in this patient from pressure on the axilla exerted by a Relton-Hall positioning frame during spinal surgery. In addition, data are presented from 15 of 500 consecutive pediatric patients who underwent surgical correction of scoliosis between 1993 and 1997 with whom intermittent monitoring of ulnar nerve SSEPs was used successfully to identify impending brachial plexopathy, a complication of prone positioning. A statistically significant reduction in ulnar nerve SSEP amplitude was observed in 18 limbs of the 500 patients (3.6%) reviewed. Repositioning the arm(s) or shoulders resulted in nearly immediate improvement of SSEP amplitude, and all awoke without signs of brachial plexopathy. This complication can be avoided by monitoring SSEPs to ulnar nerve stimulation for patients placed in the prone position during spinal surgery.