Ankylosing spondylitis is a common disease. A study conducted by our department five years ago found that the diagnosis of ankylosing spondylitis patients was delayed by an average of six years. This indicates, to some extent, that the early symptoms of the disease are not obvious and that there is still a lack of awareness of the disease in the country. Most cases of ankylosing spondylitis are relatively mild and do not usually result in serious adverse consequences. A small percentage of patients with ankylosing spondylitis may have more serious outcomes, and there are often clinical “red flags” in these patients that are worth being aware of. Danger sign 1: Thigh root pain. Ankylosing spondylitis is usually characterized by low back pain, hip pain, knee pain, and heel pain. Thigh pain is uncommon, but is often a sign of hip joint pathology. Hip lesions are prone to sequelae, i.e., destruction of hip bones, narrowing of the gap, and fusion, which can lead to inability to walk and require surgery (joint replacement) in the long term. Knee pain and heel pain, on the other hand, are not a cause for concern, as these areas are often “swollen and painful, but they are fine after treatment” and generally do not have residual sequelae. Danger signal 2: The age of onset is small. According to the statistics of our department, the younger the patient is, the more likely he/she is to develop hip arthropathy, the danger of which is described above. Danger sign 3: Early onset of hunchback. If hunchback occurs before the age of 30 (even if it is mild), you should pay attention to it. Because we are afraid that the hunchback will become more and more severe and affect the appearance and function. Danger sign 4: Decreased chest expansion. Our normal breathing depends on the contraction and expansion of the thorax. When chest expansion decreases, lung function will be affected to a certain extent. The effect is particularly pronounced in cases of pneumonia, bronchitis, or old age and frailty. Danger sign 5: The presence of heart valve pathology or kidney pathology. May affect normal life expectancy (usually normal in patients with ankylosing spondylitis). These need to be understood by means of cardiac ultrasound, urinalysis (sometimes requiring a kidney biopsy), etc.