Menstruation at the age of 10 may be normal or abnormal, and menstruation indicates sexual development. The earliest sexual development in normal children is breast development, and the interval between breast development and the first menstruation is usually 2-2.5 years. If a 10-year-old child has menstruation, it is presumed that the breast development is 8 years old or before 8 years old, and the development of secondary sexual characteristics of the breast before 8 years old means that there is precocious sexual maturity, so it is possible that a 10-year-old girl who has menstruation is abnormal. At this time, the child should be seen by a pediatric endocrinologist for a skeletal age check and to assess whether the hypothalamic-pituitary-gonadal axis is starting early. If it is, further tests should be done to clarify the cause and a cranial MRI should be done to see if the hypothalamus and pituitary gland are abnormal. If there is no abnormality, it may be true precocious puberty, which requires intervention to inhibit the premature activation of the gonadal axis. Drug intervention can be performed, most commonly gonadotropin-releasing hormone analogs, to inhibit precocious puberty and achieve a height similar to that of children of the same age without the occurrence of dwarfism, because precocious puberty mainly affects height, resulting in a lower height than that of peers.