BACKGROUND Postpartum hemorrhage remains one of the main causes of maternal morbidity and mortality in both developed and developing countries. Hemorrhages account for 28%of all direct maternal deaths and remain the most common cause of direct maternal deaths worldwide. OBJECTIVE To study the incidence and risk factors for postpartum hemorrhage (PPH) in Bhunibol Adulyadej Hospital. METHODS Retrospective cohort study of 19,429 patients who gave birth between P' January 2004 and 31st December 2007 at Bhumibol Adulyadej Hospital. One thousand five hundred and thirty women were enrolled in the present study, three hundred and eighty five women had postpartum hemorrhage and one thousand one hundred and forty-five had no postpartum hemorrhage. The present study analyzed one postpartum hemorrhage woman compared to three women who gave birth in nearly the same period and had no postpartum hemorrhage both vaginal deliveries and cesarean section. RESULTS The PPH rate in Bhumibol Adulyadej Hospital was 1.98%. Maternal age, height and fetal birth weight were not different between the PPH group and no PPH group. The strongest risk factors for postpartum hemorrhage in the present study were prolonged 3rd stage of labor, retained placenta, lacerations of birth passage, and placenta previa. CONCLUSIONS The strongest risk factors for postpartum hemorrhage in the present study were prolonged 3rd stage of labor, retained placenta, lacerations of birth passage, and placenta previa.