Abstract: The clinical and laboratory manifestations of 59 patients with juvenile ankylosing spondylitis （JAS） were analysed and compared with those of 49 ankylosing spondylitis （AS） patients. The results showed that the age of onset in JAS was 4 to 16 years with a peak of 12 to 15 years. The male to female ratio was 19∶1. Joints of the lower extremity were much more commonly affected than the upper. Three fourth of the patients had a polyarticular onset with an asymmetrical pattern of peripheral joint involvenent. The positive rate of HLA B27 of JAS patients was 88.1% and virtually all patients presented no rheumatoid factor and anti nuclear antibody. The ocular, cardiac and pulmonary involvement of JAS patients were similar to those of AS patients. Our study indicated that the most prominant differences between JAS and AS were∶1. Fewer patients with JAS had pain or stiffness in the lumbarsacral spine at onset （P ＜0.01）;2. With few exceptions, patients with JAS eventually developed peripheral joint diseases if they did not have them at onset; 3. Enthesitis occurred with greater frequency than in adult onset AS. The diagnosis, treatment and prognosis of JAS were also discussed briefly.