Variations in the length of menstrual cycle as well as duration of menstrual flow are broad and common during adolescence. They are mainly caused by the immaturity of the hypothalamic-pituitary-ovarian axis. Normalization of ovulation during the first postmenarcheal years will gradually regularize the menstrual cycle. Several medical conditions, endocrine disturbances or medical treatments may affect the hormonal balance and cause abnormal bleeding. If anemia exists, the possibility of bleeding disorder should be considered. After proper evaluation, most abnormal bleedings in adolescents can be managed hormonally, with the addition of hemostatic therapies when necessary. Oral contraceptives are most commonly used.