Abstract: Abnormal vaginal bleeding is an important cause of morbidity in women, especially during reproductive period. In this first article of our series, will be discusses in detail possible aetiology of abnormal vaginal bleeding. We will focus on uterine bleeding as a response to sexual hormones, abnormal vaginal bleeding complicating pregnancy, abnormal vaginal bleeding of pelvic cause, dysfunctional uterine bleeding and abnormal vaginal bleeding of extra pelvic causes. Keywords: abnormal vaginal bleeding