A prospective study with subjective evaluation of shoulder pain and objective evaluation of shoulder muscle strength by isokinetic testing and electromyographic and electroneurographic studies of spinal accessory nerve function was performed on patients who had undergone neck dissection procedures. Twenty-one patients with head and neck cancer were enrolled in this study. Three types of neck dissection were performed: 7 selective neck dissections, 9 modified radical neck dissections, and 5 radical neck dissections. All patients who underwent radical neck dissection had shoulder pain, and 80% of them had shoulder droop after the operation. In the patients who underwent selective neck dissection, the electromyographic findings of the spinal accessory nerve were relatively normal. Their shoulder strength was sometimes decreased at I month after operation, but it had returned to preoperative strength by the 6-month follow-up visit. These findings suggested that patients who underwent selective neck dissection had the least damage to spinal accessory nerve function and the least shoulder disability after neck dissection.