Ankylosing spondylitis is a chronic inflammatory disease which most frequently affects the sacro-iliac joints of young men, and also the synovial joints of the whole spine. Bony fusion of these joints and ossification along the longitudinal ligaments lead to total immobility of the vertebrae. Sixty-two cases of ankylosing spondylitis treated at the Severance Hospital from June 1980 to June 1986 were analysed clinically and the followings were obtained. 1. The average age was 38 years and the sex ratio between the male and the female was 58: 4(Male=94%). 2. The most frequent location of pain was low back (32%), and the pain was usually bilateral (81%). 3. The main stiff regions were the hip joint (35%) and the lumbar spine (27%). 4. The most frequent joint affected was the hip (44%), and the extraarticular manifestations were pleuropulmonary disease (29%), gastrointestinal disorder (15%), iritis (10%), etc. 5. The characteristic X-ray findings were sacro-iliac changes (72%), facet joint blurring (53%), and syndesmophyte (37%). 6. Laborstory findings showed increased ESR (85%), positive HLA B-27 (97%), negative rheumatoid factor (94%), and the serum immunoglobulins snd complements were not decreased.