The 16-year-old girl’s menstrual period is long and small, and it may be related to physiological factors, anemia, and endocrine disorders. 1. Physiological factors: 16-year-old girls are in puberty, this time may not have established a regular menstrual cycle; coupled with the usual study or life may be too much mental stress, irregular diet, etc., may lead to menstrual abnormalities. 2. Anemia: If the patient has a poor diet or anemia, it may lead to a decrease in blood circulation, so the menstrual flow is low and the menstrual period is long. 3. Endocrine disorders: If the patient suffers from endocrine-related diseases, such as polycystic ovary syndrome or abnormal development of ovarian function, it may lead to damage to the uterine lining, resulting in scanty and prolonged menstruation. There are many other reasons why menstruation may be scanty and prolonged. Excluding physiological factors, it is recommended that the patient consult a doctor in a timely manner, complete the relevant examinations, and receive symptomatic treatment under the guidance of a specialized doctor.