Neurological complications of ankylosing spondylitis (AS) are reported in 2.1% of patients. Cauda equina syndrome (CES) is rare and occurs at the ankylosing stage. MRI and CT of the lumbar spine show a cauda equina deformation with dural ectasia and bony erosion. We report three patients with AS presenting with progressive CES. These patients underwent lumboperitoneal shunting (LPS) surgery. The motor deficit improved in all cases. We suggest that CES develops from arterial pulsation of the CSF on a dural sac with reduced elasticity and that LPS reduces these intradural pressure shock waves. A meta-analysis by Ahn et al. [Ahn NU, Ahn UM, Nallamshetty L, et al. Cauda equina syndrome in ankylosing spondylitis (the CES-AS syndrome): meta-analysis of outcomes after medical and surgical treatments. J Spinal Disord 2001;14:427-33] concludes that surgical treatment has a better outcome than conservative or no treatment. Adding our 3 patients to this analysis, it appears that LPS for CES in AS is more efficient than laminectomy. LPS is a routine procedure for a rare indication, which promises improvement or atleast a stabilization of this disabling evolution of the disease.