The diagnosis of ankylosing spondylitis requires fulfillment of clinical and radiologic criteria as well as serologic criteria. Clinical criteria require the presence of low back pain and morning stiffness for more than 3 months, and significant limitation of lumbar spine motion and lower than normal thoracic mobility. Radiologic criteria require X-rays showing sacroiliac arthritis, and serologic diagnostic criteria are a positive blood HLA-B27 serologic test. Ankylosing spondylitis is identified if radiologic criteria and one clinical criterion are met. Radiologic criteria alone or clinical criteria alone do not establish ankylosing spondylitis, but it is suspected that ankylosing spondylitis may be present. In the early stages of ankylosing spondylitis, medications should be used systematically, including nonsteroidal anti-inflammatory drugs, biologics, and chemotherapeutic agents. During the non-acute exacerbation period, it is important to strengthen the functional exercises of the joints and try to preserve the joint functions.