If a woman does not menstruate for three months, medically this is called amenorrhea. If she is relatively young, it is essential to visit a hospital for relevant examinations. Generally, an ultrasound is conducted first to check the thickness of the endometrial lining and to assess if there are any organic diseases affecting the uterus or ovaries. If the endometrium appears thin and there are no organic diseases, further examinations should include tests for six sex hormones, which are indicators of ovarian function. If the results suggest premature ovarian failure or some endocrine disorders, treatment can be tailored according to these findings. Moreover, if the woman has reached menopausal age and indeed has not menstruated for three months, this condition is considered amenorrhea, which might be physiological. Hence, if an older woman experiences amenorrhea, it is likely true menopausal amenorrhea. Additionally, if a woman who normally has regular menstrual cycles does not menstruate for three months, pregnancy cannot be ruled out, and it is crucial to conduct relevant tests for early pregnancy.