Hip synovitis is the most common cause of hip pain in children and always makes parents feel scared, resting for a while to get better, and then a few days later the child starts limping with pain again. Some parents are aware of this and are always afraid that it will progress to childhood femoral head necrosis. Synovitis of the hip joint is called “acute transient or self-limiting synovitis of the hip joint”. As the name implies, this inflammation can get better on its own. However, when diagnosing hip synovitis, it is important to exclude septic arthritis, which requires emergency treatment, often with high fever, localized joint swelling and pain, skin redness and swelling, and other changes that can be clarified by blood tests and MRI. Hip synovitis may sometimes be a precursor to femoral head necrosis, juvenile-type arthritis, and compulsory spondylitis in children. Recurrent episodes require vigilance for the presence of corresponding irritating lesions, usually with corresponding other manifestations. On average, 2 out of 10,000 children develop hip synovitis each year, and 3 out of 100 children have hip synovitis throughout childhood (1-13 years), with a recurrence rate of about 4%. It is more common in boys than in girls and is more likely to occur between the ages of 4 and 10 years, with a peak age of 6 years. The etiology of hip synovitis is unclear, and some may be secondary to a viral cold, manifesting as a sudden limp or refusal to move to the floor. After excluding septic arthritis and keeping the child at bed rest, the symptoms of hip synovitis will improve spontaneously. The duration of the disease usually does not exceed 2 weeks, and about half of the children recover completely within 1 week. During the gradual recovery process, if the child wants to stand and walk, there is no need to restrict the child too much. For children who are more active, normal activities should be resumed gradually. Hip synovitis is a cause of femoral head necrosis in children, but there is no accurate quantitative assessment of the specific risk. In case of recurrent episodes and significant limitation of hip movement, standard pelvic orthopantomographs and frog films should be taken to determine whether there are early signs of femoral head necrosis.