Background To identify risk factors for severe postpartum hemorrhage (PPH) ≥1000 ml in women giving birth vaginally. Method A register‐based cohort study including women with singleton pregnancies giving birth vaginally at term to a live‐born child at Aarhus University Hospital, Denmark, from January 1, 2004, to December 31, 2012. Logistic multivariable regression was used to analyze data. Results In 31 837 births, 1832 women (5.7%) experienced severe PPH. Maternal age, smoking during pregnancy, and prepregnancy body mass index did not increase the risk of severe PPH. However, nulliparous and multiparous women with a previous cesarean birth had an increased risk of severe PPH. Antepartum and intrapartum risk factors for severe PPH included gestational age >40 weeks, induction of labor, augmentation of labor, irregular fetal position, instrumental birth, and birthweight >4000 g. In particular, the combination of induction and augmentation of labor doubled the risk of severe PPH. Among genital tract tears, vaginal tears >3 cm were associated with the highest risk of severe PPH. Conclusions Maternal characteristics did not increase the risk of severe PPH, except for nulliparous and multiparous women with a previous cesarean birth. Obstetric interventions such as induction of labor, augmentation of labor, and a birthweight higher than 4000 g increased the risk of severe PPH. Larger vaginal tears presented the highest risk of severe PPH. Clinical practice with rigorous indications for obstetric interventions and timely identification and management of genital tract tears may reduce risk of severe PPH.