Ankylosing spondylitis may affect the spine segmentally or diffusely. Because all the ligaments become ossified in the involved areas, fractures that occur through this involved segment traverse both bone and ligaments, producing an extremely unstable situation similar to a shearing type of fracture. With a pre-existing severe kyphosis, it may be dangerous to turn the patient to a supine position, because this opens up the fracture and can cause neurologic complications. The radiologic assessment of the spine in ankylosing spondylitis is difficult because the bone is frequently osteoporotic and the disc spaces are poorly outlined. Minor displacements should be looked for, as well as discontinuity of ossified ligaments (especially the interspinous ligaments). Of the seven patients reported in this series, six had fractures undiagnosed at the time of the preliminary examination. Therefore, patients known to have ankylosing spondylitis should be counseled regarding the possibility of a fracture, and if pain persists after an injury, they should be thoroughly investigated radiologically to rule out a potentially serious problem. Reduction of the displacement and stabilization is best achieved with a Luque rectangular rod system, and laminectomy is not indicated.