Forty-seven operations for posterior fusion of the upper cervical spine were reviewed for complications. Alarmingly, only 11 patients had an entirely uncomplicated course. Most complications were minor, but there were four nonunions, one requiring reoperation. Although seven patients had increased neurologic deficits after surgery, only one was permanent. There was one death due to technical error. Patients with significant instability, myelopathy, prior failed fusions, or unreducible dislocations are at high risk for perioperative neurologic complications.