There are two possibilities for increased sacroiliac bone density. The first is the occurrence of osteoarthritis, where the increased density causes unevenness of the joint surface between the sacrum and the iliac bone, which produces pain when moving, and usually feels stiff and uncomfortable. The other reason is ankylosing spondylitis, which requires a combination of laboratory blood tests. If CT shows increased density of the sacroiliac bone and positive blood B27, the possibility of ankylosing spondylitis is relatively high. The main risks for the future are fusion of the joints, restricted movement, and fusion of the lumbar spine, which can affect life to a certain extent. Therefore, if the density of the sacroiliac joint is increased, a detailed examination must be performed to give early treatment.