Twenty years old menstruation does not come for several months may be physiological causes, hypothalamic factors, pituitary factors, ovarian causes and uterine causes. 1. Physiological causes: such as pregnancy, pregnancy will have a history of obvious menopause, can be clearly diagnosed by blood hCG (human chorionic gonadotropin) level measurement, ultrasound, obstetric examination, and so on. 2. Hypothalamic causes: such as mental stress, weight loss, locomotor amenorrhea and drug-induced amenorrhea, etc., which can be diagnosed through medical history, MRI or CT examination. 3. Pituitary causes: such as pituitary infarction, pituitary tumors and empty saddle syndrome, etc., which can be diagnosed by medical history, CT or MRI, X-ray examination, etc. 4. Ovarian causes: such as premature ovarian failure, functional ovarian tumors, polycystic ovary syndrome, etc., which can be diagnosed by endocrine examination and ultrasonography. 5. Uterine causes: such as multiple abortions, excessive scraping and other causes of uterine adhesions, post-abortion infection, puerperal infection, etc., can be combined with the history and ultrasound, endocrine examination, etc. to assist in the diagnosis. Twenty years old menstruation a few months do not come to the time to go to the hospital in order to identify the cause, and active treatment.