The severity of ankylosing spondylitis varies greatly in different people. About two-thirds of patients have mild disease and another third have severe disease (or will progress to severe later). The author presents here some of the characteristics of severe cases, which are also the focus of our work, in the hope that they will help you further understand your condition. Feature 1: Hip joint lesions (thigh root pain) Unlike other races in the world, in the Chinese population, hip lesions that are not treated actively in time are likely to cause destruction of hip bones, narrowing of joint joints, fusion, and long-term development will affect going to the toilet, climbing stairs, and even walking, and the most desperate can only be “joint replacement”. Feature two: the age of onset is small. The disease has a general rule that “the older you are, the lighter the inflammation, and the inflammation slowly subsides after forty years old”. A very young onset (e.g., teenage years) suggests a high degree of inflammation, and the longer the inflammation lasts, the more severe the accumulated bone destruction. Younger patients are also prone to hip arthropathy (see above for risks). Generally speaking, the younger the onset, the greater the likelihood of disability later on. Feature 3: There is a family history of the disease. For example, if a father and son have the disease at the same time, or if brothers have the disease at the same time, there are obvious genes that cause the disease in these cases, and their overall condition is more serious than that of disseminated cases. Feature 4: The doctor judges that he or she has had the disease for a long time, but the pain is suddenly severe. In these cases, the inflammation is mild at the beginning, but after a period of time, the disease suddenly worsens, like a “volcanic eruption”. This is the key time for treatment, and timely and active treatment can promote the basic dissipation of inflammation and reduce bone destruction. Feature 5: Neck pain and back pain. The development of the disease is generally “bottom-up”, starting from the buttocks, lower back slowly upward to the back and neck, once the neck pain appears, it is likely that the disease has spread to the uppermost spinal segments, so it needs to be taken seriously. Feature 6: Early onset of hunchback. If hunchback occurs before the age of 30 (even if it is relatively mild), it should be taken seriously. If the cervical spine is affected and the head cannot be lifted, the eyes can only keep looking at the ground, which seriously affects life and work. Feature 7: Laboratory tests suggest significantly elevated inflammatory indicators. Generally, the inflammatory indexes of patients, such as blood sedimentation and C-reactive protein, are only mildly elevated or normal. If they are significantly elevated (e.g., several times higher), it suggests that inflammation in the body is more pronounced and treatment should be intensified. AS patients with one or more of the above characteristics should pay sufficient attention to avoid delaying treatment.