Anterior cervical spine fusion was carried out on 443 cases between 1965 and 1988 with pseudarthrosis or delayed union in 15 (3.4%). The causes of these complications were malalignment and faulty postoperative care. Symptoms resulted from abnormal mobility, cord compression due to posterior slip or rotation of the upper vertebral body, kyphotic deformity or a problem at the adjacent level. Four out 5 cases with symptoms recovered successfully after a second operation.