Dysfunctional uterine bleeding is defined as abnormal endometrial bleeding without structural pathology. Although, abnormal uterine bleeding may occur in women of all ages, it is a particularly common issue for adolescents. This article reviews the normal menstrual cycle and the abnormal menstrual cycles. Familiarity with the normal menstrual cycle is necessary to identify the possible causes of abnormal bleeding and aids in the diagnosis and treatment of patients with abnormal uterine bleeding.