The thickness of the endometrium varies at different times of the menstrual cycle in women. Generally the endometrial thickness should be less than 15-20 mm in the week before menstruation in young women and 5 mm in menopausal women, and more than this is considered endometrial thickening. Endometrial thickness above normal should be taken seriously and requires curettage and cytopathological diagnosis if necessary. If the endometrial thickness is at a critical value it should be reviewed frequently. In some young women, the thickness of the endometrium is related to the physiological cycle and can be thick or thin, so ultrasound should be performed at different times of menstruation and high values should be examined further by a doctor.