Menstruation once every two months may be a manifestation of a long normal menstrual cycle, or it may be caused by hyperthyroidism, polycystic ovary syndrome, menstrual disorders and other reasons. 1. Normal long menstrual cycle: Women who experience menstruation once every two months may do so because they have a long menstrual cycle, such as a 35-day menstrual cycle, which may manifest itself as the next menstrual period coming in the second month of the last menstrual period. 2. Hyperthyroidism: the phenomenon of menstruation coming once every two months may also be a manifestation of scanty menstruation when a woman suffers from hyperthyroidism and other endocrine disorders. In addition to scanty menstruation, a woman may also have symptoms such as hand tremor, fast heart rate, shortness of breath, and loss of weight. 3. Polycystic Ovary Syndrome (PCOS): Women who have menstruation once every two months may also suffer from PCOS. In addition to scanty menstruation, women may also suffer from scanty menstruation or even infertility. 4. Menstrual disorders: Menstruation once every two months may also be a sign of menstrual disorders. A woman may be under a lot of stress and tension in her life, which can lead to menstrual disorders. The cause of menstruation can not be accurately determined solely on the basis of a woman’s menstruation once every two months, but also needs to be combined with the characteristics of the medical history and other test results to make an accurate judgment, and it is recommended to clarify the cause of the disease under the guidance of a doctor.