The outcome of total hip replacement (THR) in ankylosing spondylitis (AS) is unclear. Concern has often been voiced by both surgeons and physicians regarding potential reankylosis, mechanical failure and poor function. We present an independent review of the patients' perception of outcome in 150 total hip replacements (138 primary + 12 revisions) in 87 subjects with AS. The mean followup was 7.5 years (1-34 years). Twelve were followed for greater than 15 years and 33 for greater than 10 years. Bilateral replacements were performed in 51 of the 87 patients (59%), 33 (65%) of whom had bilateral surgery within a 12-month period. Failures were early and rare. Twelve of 138 (9%) were revised (8 patients, mean of 3.6 years postoperatively) and 3 of the 12 were rerevisions. Twelve total hip replacements followed for 15 years or more resulted in only 2 failures (same patient: reankylosis) while 3 failed out of 33 followed for 10 years or more. Overall, for the 138 total hip replacements in situ (including the revisions), the patients considered outcome to be good or very good in 86%, while 89% had no (63%) or mild (26%) pain. Mobility was good or very good in 44%. On a scale of 1-5 (very poor to very good) patients followed for up to 5 years scored 4.7, as did those followed for greater than 15 years. Sixty-nine percent of the male recipients under age 60 are at work. Reankylosis occurred in only 1 patient (4 hips). In general the first and second hips replaced had an equally good outcome. The long-term outcome of total hip replacement in AS is very good. The few failures occurred early, and patients were as satisfied with the outcome more than 15 years postoperatively as they were within the first 5 years.