Ankylosing spondylitis is reported to involve not only the joints but other organs as well. Among these extra-articular involvements, uncommon complications associated with nervous system such as single root lesions, compression of the myelum and cauda equina syndrome have also been documented. Here we present a patient with long-standing ankylosing spondylitis who developed spastic paraparesis. Extensive study to find the cause of a spastic paraparesis failed and therefore led to the conclusion that this patient was suffering from transverse myelitis. Similar reports in the past have been attributed to an association with multiple sclerosis; however, we suggest that the findings support the diagnosis of a rare complication of ankylosing spondylitis with an unknown etiology.