The absence of menstruation in girls is an abnormal manifestation for many reasons that need to be carefully identified: first, primary amenorrhea, the absence of menstruation all the time after puberty is mostly seen in abnormalities of the reproductive tract, such as congenital vaginal atresia, vaginal transverse septum, which is a blockage of the channel, so that menstrual blood cannot flow out, or congenital absence of vagina, absence of uterus, inability to produce menstruation, and gender dysphoria, which also does not produce menstruation; second, secondary amenorrhea, the presence of menstruation during puberty, and later not coming for various reasons, which is called secondary amenorrhea. This is called secondary amenorrhea, most commonly due to gynecological endocrine abnormalities, such as polycystic ovary syndrome, which may result in sporadic menstruation, prolonged cycles or even three to six months without menstruation. Amenorrhea due to damage to the endometrium and adhesions in the uterus as a result of multiple uterine surgeries, endocrine diseases of internal medicine such as thyroid function, other factors, amenorrhea caused by overwork, overexercise, extreme malnutrition, chemotherapy, endometrial tuberculosis, radiotherapy, etc. In special cases, amenorrhea may be caused by the use of oral progestin, birth control pills, intrauterine placement of medicated contraceptive rings, skin implant contraception, etc. Menstruation will resume soon after stopping the medication.