Twenty-four patients with surgical section of the accessory nerve and/or its cervical contribution(s) were examined from 1 to 156 months after surgery, and compared to twenty controls. Thirteen patients had a classical neck dissection; seven had the whole length of the accessory nerve preserved but not the cervical plexus contributions. Four had the upper half of the accessory nerve sectioned, but with preservation of both the lower half and its cervical contributions. Clinical and electrophysiological studies of the three portions of the trapezius suggested the existence of an undescribed motor nerve supply to the trapezius and of a motor input from the cervical plexus contributions via the accessory nerve. The former is also supported by an anatomical study.