Vacation refers to menstruation. Fifteen-year-old girls who have not had menstruation for half a year can be considered as having irregular menstruation during puberty, pregnancy or amenorrhea, which can be related to etiology such as locomotor amenorrhea, mental stress or pituitary tumors. 1. Irregular menstruation during puberty: During the puberty stage, irregular ovulation and irregular menstruation can occur because the ovarian gonadal axis of women is not yet well developed. 2. Pregnancy: If a woman has a history of sexual intercourse, she should consider whether it is pregnancy. After pregnancy, there will be symptoms such as menopause and early pregnancy reaction, so there may be no menstruation for half a year, at this time, the level of human chorionic gonadotropin in the blood is elevated, and ultrasonography can also be detected. 3. Amenorrhea (1) Exercise amenorrhea: women who have long-term strenuous exercise or training such as ballet may have body fat loss, malnutrition and other physical changes, which may cause amenorrhea due to the inhibition of the function of the reproductive axis. (2) Mental stress: in long-term mental tension, depression or environmental changes, emotional changes, due to the emergence of neuroendocrine dysfunction, the pituitary gland secretion of gonadotropins and the hypothalamus secretion of gonadotropin-releasing hormone is inhibited, thus causing amenorrhea. (3) Pituitary tumors: when a tumor occurs in the pituitary gland located in the pterygoid saddle, such as when an adenoma occurs that secretes prolactin, prolactin inhibits the hypothalamus from secreting gonadotropin-releasing hormone, which can lead to the occurrence of amenorrhea. If a 15-year-old girl does not have menstruation for a long time, it is recommended that she go to the hospital to consult a specialist in a timely manner for a clear diagnosis and symptomatic treatment of the cause.