We conducted a study to evaluate the hypothesis that the preservation of cervical root branches of the cervical plexus is associated with greater shoulder mobility, less loss of face and neck sensation, and better quality of life (QoL) following functional neck dissection in which the spinal accessory nerve is spared. We also investigated the impact of postoperative physiotherapy on these three outcomes. Our study population was made up of 54 patients-47 men and 7 women, aged 34 to 78 years (mean: 53.4)-who had undergone functional neck dissection as a treatment for head and neck cancer over a 3-year period at our institution. Patients were divided into two groups: 23 patients whose cervical root branches were preserved during surgery (preservation group) and 31 whose branches were removed (removal group). Shoulder mobility was measured by the Arm Abduction Test (AAT), face and neck sensation was assessed by fingertip touch in eight areas of the head and neck, and QoL was determined by the University of Washington-Quality of Life questionnaire (UW-QoL4). The AAT revealed that the preservation group had significantly better shoulder mobility. The fingertip touch evaluation revealed significantly less loss of sensation in Saffold regions A and D. Analysis of the UW-QoL4 results revealed that the preservation group experienced significantly less pain, significantly fewer shoulder complaints, and significantly fewer limitations on activities and recreation, as well as significantly better health-related and overall QoL. The preservation group also had a significantly better composite score, global score, social function score, and mood and anxiety score on the UW-QoL4 assessment. Finally, we found that physiotherapy improved both QoL and shoulder mobility, although these improvements were not statistically significant. We conclude that preservation of the cervical root branches significantly improves outcomes in patients who undergo functional neck dissection.