Puerperal uterine inversion is a severe but rare obstetric complication of yet unknown origin. In this two-year study we determine the incidence of this complication and we describe associated risk factors to expose its etiology. All cases of uterine inversion were included from a nationwide cohort study which contained all 98 hospitals with a maternity unit in the Netherlands. We reviewed the medical records of 15 patients, resulting an incidence of approximately 1 in 20 000 vaginal births. Fourteen cases (93.3%) were classified as low-risk pregnancies at booking. Nulliparous women were not overrepresented and the main associated factors were signs of prolonged labor followed by third stage manipulation. This study is the first population-based study for uterine inversion. With the reported associated factors and occurrence in women with a low-risk profile, we show that every birth attendant should be able to detect this rare but severe complication. © 2012 The Authors Acta Obstetricia et Gynecologica Scandinavica © 2012 Nordic Federation of Societies of Obstetrics and Gynecology.