Cranial diabetes insipidus (DI) due to postpartum haemorrhage is an extremely rare clinical event. We describe herein isolated posterior pituitary insufficiency in a 26-year-old woman who had undergone subtotal hysterectomy for severe postpartum haemorrhage because of uterine rupture. The patient experienced polyuria within 6 h postoperatively. DI was suggested by the elevated urine volumes and low urine specific gravity. The diagnosis of DI was confirmed by water deprivation test and vasopressin stimulation test. The anterior pituitary function was within normal limits. A high clinical suspicion is certainly required for the diagnosis of DI in the immediate postpartum period. To rapidly initiate appropriate therapy, the possibility of DI should always be kept in mind while evaluating patients who have polyuria and polydipsia after severe postpartum bleeding. Delay or failure to treat this condition might result in hypovolemic shock.