Three cases of cauda equina syndrome in long-standing ankylosing spondylitis are reported. In all, vertebral scalloping and dural ectasia were confirmed by magnetic resonance imaging and computed tomography. MRI showed widening of the dural sac with signal intensity corresponding to cerebrospinal fluid. CT demonstrated asymmetrical lesions of the posterior elements of the lumbar spine. Myelography was not felt necessary to confirm the findings.