With the popularity of internet knowledge, many patients come to our clinic with HLA-B27 test results and ask, “I have a positive result, does that mean I have ankylosing spondylitis? HLA-B27, also known as human leukocyte antigen-B27, has been shown to be closely related to the development of ankylosing spondylitis. However, according to clinical epidemiological surveys, the incidence of ankylosing spondylitis in HLA-B27-positive individuals is about 10%-20%, while the incidence in the general population is 1‰-2‰, and the rate of HLA-B27 positivity in patients with ankylosing spondylitis is as high as 90%-96%, while only 4-10% of the general population is positive. It is not the only factor affecting the disease. The diagnosis must be combined with the patient’s symptoms, signs and imaging such as CT of sacroiliac joint in order not to misdiagnose the disease.