Fifty-two patients with traumatic spondylolisthesis of the axis were admitted to the University of Maryland Spinal Injury Center between 1977 and 1982. There were fifteen Type-I fractures, twenty-nine Type-II fractures, three Type-IIa fractures, and five Type-III fractures. Associated neurological deficits were found in only four patients, although unassociated neurological deficits such as closed head injury were seen in eleven patients. Thirteen patients had other fractures of the cervical spine. Type-I fractures were stable injuries and were treated with collar protection. Most Type-II injuries were reduced with the patient in halo traction, and then immobilization in a halo vest was used. Type-IIa injuries, as they showed increased displacement in traction, were reduced with gentle extension and compression in a halo vest. Type-III injuries were grossly unstable and required surgical stabilization. All of the fractures healed, although the use of early halo-vest immobilization for displaced fractures resulted in significant residual deformity. The radiographic patterns of the fracture types and the resulting data on clinical stability suggested a correlation between the fracture type and the mechanism of injury. Type-I injuries resulted from a hyperextension-axial loading force; Type-II injuries, from an initial hyperextension-axial loading force followed by severe flexion; Type-IIa injuries, from flexion-distraction; and Type-III injuries, from flexion-compression.