The aim of this study was to clarify the morphological characteristics of the communicating branch between the spinal accessory nerve and the anterior root of the first cervical nerve (McKenzie branch), a structure severed during intradural selective rhizotomy for treatment of spasmodic torticollis. The right and left sides of 50 upper cervical segments of spinal cords were dissected and examined under a surgical microscope. Seven of the total 100 samples were found to have the McKenzie branch. Two types of McKenzie branch, which run close to the vertebral artery, were also identified, which might be helpful for improving the surgical results of intradural selective rhizotomy.