Lethal aortic injury as a result of fracture of the lumbar spine in a patient with ankylosing spondylitis is reported. This complication is a direct result of the pathophysiologic changes of ankylosing spondylitis that cause the aorta to become firmly adherent to the anterior longitudinal ligament. Recognition of the potential for this injury in patients with ankylosing spondylitis should prompt early investigation of the integrity of the aorta and planned reconstructive surgery for this potentially lethal injury.