Bone age can effectively reflect the maturity of the human body, and its advancement or lagging relative to the actual age can determine the type of growth of children, and has an important impact on adult height and the first menstruation of girls, etc. Therefore, bone age evaluation has a wide range of uses in clinical medicine, and is an important aid in the diagnosis, differential diagnosis and observation of the efficacy of many diseases affecting the growth and development of children. In pediatric clinics, it is mainly used in the following areas: (1) Abnormal thyroid function Thyroid hormone is indispensable for skeletal growth and maturation, and hypothyroidism will delay bone development, underdevelop the long bone epiphysis, and make the limbs too short and become dwarf. Therefore, the bone age of children with hypothyroidism is lower than the actual age. During treatment with thyroid hormone the bone age development is accelerated, showing the phenomenon of catching up growth. Excessive doses of thyroid hormone can have effects similar to those of hyperthyroidism, causing a certain degree of advancement in bone development, i.e., a bone age greater than the actual age. (2) Growth hormone deficiency Growth hormone promotes bone growth through insulin-like growth factors, so children with growth hormone deficiency have abnormally delayed bone age, usually by more than two years, and are abnormally short in stature. However, some drugs such as certain sex hormones or nutritional products containing sex hormones, although they can promote the growth of the child’s height at that time, at the same time accelerate the growth of the bone age and promote the early closure of the epiphysis, which will eventually reduce the child’s final height. Therefore, it is necessary to use these drugs under the guidance of a doctor. (3) Precocious puberty and sexual infantilism Both pathological and somatic precocious puberty are associated with early bone age. As a result of early epiphyseal healing, they become shorter in adulthood. Children with sexual infantilism have significantly delayed puberty, causing delayed bone age due to hypogonadism. The prediction of bone age and adult height is an important monitoring method in the treatment of these disorders. Bone maturity and height growth rate kept as close to normal as possible are the best indicators for monitoring the treatment process. (4) Systemic diseases Systemic diseases in children are likely to cause delayed bone development, such as gastrointestinal diseases with impaired nutrient absorption, metabolic diseases and renal diseases. Malnourished children have delayed bone development and a significantly higher rate of epiphyseal abnormalities in the wrist. Therefore, if epiphyseal abnormalities are found on hand X-rays, children should be examined for endogenous or exogenous growth disorders. (5) Normal variation In children with non-pathological short or tall height below the 3rd percentile of normal standards or above the 97th percentile, bone age is one of the main indicators to decide whether to treat and to evaluate the effectiveness of treatment. Bone age examination is also an important tool in determining the type of pubertal development and maturity. Bone age determination is used to determine the age at which pubertal growth begins to accelerate, to predict adult height and the age of menarche in girls, and to help explain the worries and doubts caused by individual growth variation during puberty.