Central diabetes insipidus (CDI) arising in the puerperal period has been attributed mainly to Sheehan's syndrome or to lymphocytic infundibulo-neurohypophysitis. We report the case of a 24-year-old woman who came to our observation for the appearance, 3 weeks after a normal delivery, of a polyuric-polydipsic syndrome. Measurements of urinary volumes, plasma osmolality and urinary osmolality, in conditions of free water intake, water deprivation and a water deprivation-vasopressin administration test, demonstrated CDI. Brain magnetic resonance imaging showed a normal morphology of the adenohypophysis and total absence of the neurohypophysis. Assays of the pituitary hormones were found to be within normal limits. These results, incompatible with a diagnosis of Sheehan's syndrome and lymphocytic infundibulo-neurohypophysis, excluded all the other known causes of acquired CDI. Our diagnosis was therefore of post-gravid idiopathic CDI. Thus, it is possible that in the puerperal period other diseases of the posterior hypophysis may develop, of unknown etiopathogenesis but equally responsible for CDI.