Rheumatic disorder involving characteristic chronic inflammation of the joints between the sacrum and the spine, between the vertebrae, and between the vertebrae and the ribs; in 25 per cent of cases the hip, knee and shoulder are also affected. The condition occurs particularly in men between the ages of 20 and 30, and is often hereditary, and probably caused by a disturbance in the immune system. The first symptoms are pain, worse at night, and stiffness in the back, leading to stiffening and deformation of the spinal column, beginning low and spreading upwards. Stiffening of the joints between vertebrae and ribs reduces mobility of the chest, causing abdominal breathing. Discomfort may reduce or increase spontaneously; the patient’s temperature usually rises in the active stage. Examination must distinguish ankylosing spondylitis from other rheumatoid conditions. X-rays show characteristic changes in the joints between spine and sacrum. Photographs of the spinal column show kyphosis, and calcification around the vertebrae, the so-called bamboo spine. Blood tests reveal the presence of certain immune substances characteristic of the complaint and other rheumatoid disorders. Treatment is by physiotherapy, remedial therapy and medication to control pain and inflammation.