Severe ectopic decidual reaction of the peritoneal surface as the etiology of unexpected intraabdominal hemorrhage is rare. Such a situation occurred in one of our patients after an uneventful vaginal delivery. The bleeding was discovered during postpartum sterilization, and hysterectomy was performed to control it. Six cases reported previously presented with peripartum shock and/or an acute abdomen. Three died, all of intraabdominal hemorrhage and two of them without laparotomy. Various etiologies of this disorder have been postulated, but a consistent explanation remains to be found. Intraabdominal hemorrhage, whatever its cause, must be controlled directly at laparotomy.