The average length of menstrual cycle is 28 days, and duration of flow is 4 days, and an average blood loss is 35cc. Abnormal uterine bleeding is defined as bleeding at abnormal or unexpected times or by an excessive flow at the time of expected menses. Any bleeding should be considered abnormal in premenarchal girls and in postmenopausal women. The etiology of abnormal uterine bleeding encompasses a wide range of disorders that can be secondary to pregnancy-related disorders, anatomic changes of the female genital tract, infection, endocrinologic disorders, malignancies, and systemic illnesses. Dysfunctional uterine bleeding (anovulatory or ovulatory) is diagnosed by exclusion of these causes. An appropriate workup is guided by age-related differential diagnoses for abnormal bleeding. Modern diagnostic tools can readily reveal the underlying pathology and allow timely intervention. Most abnormal genital tract bleeding occurs in the form of uterine bleeding, which is one of the most common gynecologic problems that health care providers encounter with, accounting for approximately 19% of office visits and 25% of gynecologic operations. The author will review the categories of abnormal uterine bleeding and the diagnostic tools needed to establish the correct diagnosis and treatment strategy.