Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease that predominantly affects sacroiliac joints and spine. It is the prototype of spondyloarthritides (SpA) and one of the most common rheumatic diseases. Sacroiliitis is the earliest manifestation of disease and accompanying with spinal involvement cause inflammatory back pain (IBP). IBP usually starts insidiously in the early adulthood and typically it is felt deep in the buttock and/or lower lumbar regions. It improves with activity and returns with the rest and is usually accompanied by morning stiffness lasting at least 30 minutes. Involvement of the spine in patients with AS is usually not limited to the sacroiliac joints and lumbar region and usually it extends up to the thoracic and cervical segment. Currently the only sign that is diagnostic for AS is radiographic sacroiliitis. However radiography detects structural changes and take up to ten years to appear unequivocally.