The clinical histories and radiographs of 28 patients with ankylosing spondylitis were reviewed. Symptoms developed before the age of 17 in all cases. Juvenile ankylosing spondylitis affected youths in their early teens, who presented most commonly with appendicular joint complaints rather than low back pain. The disease was progressive, with the characteristic changes of ankylosing spondylitis eventually occurring in the spine and sacroiliac joints, frequently accompanied by widespread and severe changes in the appendolar joints. HLA B 27 antigen was present in 8 of the 9 patients tested. Thorough clinical, radiographic, and laboratory examination should prevent confusion with juvenile rheumatoid arthritis.