Irregular menstruation in 18-year-old girls can be a normal condition. This is because an 18-year-old girl may be in the age of puberty. In adolescent females, the biological axis is not completely sound at this time. The thalamus-pituitary-ovary axis cannot form normal feedback and the ovaries cannot ovulate regularly, so irregular ovulation results in irregular menstrual cycles. Clinically, if there are no other combined abnormalities, no special treatment is needed. If there are other clinical symptoms such as dizziness, nausea, vomiting, and weakness, it is important to go to the hospital as soon as possible for appropriate examination in order to exclude the possibility of other diseases. With the disappearance of puberty, normal menstrual cycle changes can occur after entering the reproductive stage.