There are many clinical causes of menstrual disorders, and the absence of menstrual flow should be considered as the first possibility of functional amenorrhea when it is determined that there is no pregnancy. The causes of functional amenorrhea can be divided into the following categories: first, hypothalamic pituitary amenorrhea. The menstrual cycle in women is regulated by a combination of factors. The brain is the higher center that regulates the menstrual cycle. When abnormalities occur in the hypothalamus as well as in the pituitary gland, it can lead to menstrual disorders. The most common of these is organic lesions of the hypothalamus and pituitary gland. Some women also experience brain dysfunction when they are under increased stress, which can affect their menstrual flow. Second, ovarian amenorrhea. Ovarian cyclic secretion of estrogen and progesterone is the key to normal menstruation. Abnormal ovarian function can cause delayed menstruation. Third, uterine amenorrhea. The endometrium undergoes cyclic shedding under the action of hormones to produce menstruation. When the uterus is diseased, it can cause a delay in menstruation. Examples include extensive adhesions in the uterine cavity. Therefore, determining the cause of delayed menstruation is the key to diagnosis as well as treatment. In summary, the absence of menstruation without pregnancy requires prompt medical attention to identify the cause and treat the problem.