Low back pain is one of the common clinical manifestations, but if it occurs in adolescents, especially in males, and is characterized by nighttime heaviness, with morning stiffness, and decreases after activity, think of spondyloarthropathy, and do not easily explain it by growing pains, cold or too much activity, but go to the rheumatology department of the hospital in time to avoid delaying the disease, and therefore remind young parents and pediatricians not to underestimate adolescent low back pain, especially lumbosacral and The pain is likely to be an early manifestation of ankylosing spondylitis and can be further examined. Once the diagnosis is made, aggressive early treatment should be given to prevent further inflammation, deformity and dysfunction. The prognosis is better if the disease is treated early and positively, the child can learn and grow as normal and will not affect future work, study, marriage and childbirth, etc. However, if the disease is not diagnosed and treated in time, the inflammation of the joint may develop progressively causing bone destruction, joint deformity, spinal ankylosis and dysfunction, affecting the normal development and future life of the child. The early treatment is half the effort, while the late treatment is half the effort, and some lesions once formed will be irreversible. For example, a male, 17 years old, came to the hospital with low back pain for 2 years. The patient had low back pain for unknown reasons 2 years ago, mainly at night, and the low back was stiff and painful when he woke up in the morning, but after getting up, the stiffness and painful symptoms gradually decreased after appropriate activities, so the parents did not mind because they heard people say it was growing pain. The above-mentioned symptoms recurred and gradually worsened, and sometimes there was alternating pain in the buttocks, and gradually there was difficulty in getting up in the morning, and the lumbar activity was limited. At this time, he went to the rheumatology clinic of the hospital. After examination and diagnosis of ankylosing spondylitis, ankylosis has occurred in the lower and upper part of the spine, indicating that the condition is not early, and after active regular treatment, although the pain is completely relieved, some of the lesions are irreversible. The majority of patients can recover completely without any sequelae if they are seen in a timely manner at the beginning of the disease, after active formal treatment. This patient had a little regret because of the late diagnosis.