We present two cases of cauda equina syndrome in ankylosing spondylitis. Cauda equina syndrome is a rare complication of ankylosing spondylitis, the pathogenesis of which is not well understood. The onset is insidious with pain and sensory symptoms; sphincter disturbances are common. After a period of increasing neurological symptoms, the condition tends to stabilize. The degree of nerve involvement is variable and can be accurately defined by electromyography. The diagnosis has to be confirmed by computed tomography (CT) or magnetic resonance imaging (MRI); myelography must be avoided. There is no specific treatment, except for pain control. The different clinical presentations and the role of new imaging techniques, CT and MRI, are demonstrated.