We conducted a prospective study of 11 patients to (1) determine the feasibility of electrophysiologic monitoring of the spinal accessory nerve (SAN) during modified radical neck dissection, (2) determine whether a threshold increase in current is required to stimulate the SAN by comparing the amount of current on initial identification of the SAN and the amount of current after completion of the dissection prior to closure, and (3) determine whether clinical outcome measures of shoulder syndrome at 72 hours and 45 days postoperatively are affected by a threshold increase. We found that 3 of 11 patients (27.3%) experienced significant threshold increases (>0.4 mA) on completion of the dissection. Of 8 patients who completed a shoulder syndrome evaluation, 3 (37.5%) had scapular winging, mild to moderate pain, and less than 90% of shoulder abduction. Two of 3 patients with shoulder syndrome had a threshold increase on electrophysiologic monitoring. We conclude that electrophysiologic monitoring of the SAN is feasible. It did not identify a threshold increase in more than 70% of patients. Electrophysiologic integrity of the SAN did not completely correlate with clinical outcome measures for shoulder syndrome.