Only a few cases of severe acute water intoxication (AWI) due to intranasal desmopressin have been reported, none of which occurred in patients with primary polydipsia. We describe a case of AWI with semicoma and convulsions, due to intranasal desmopressin, in a 32-year-old patient with dipsogenic diabetes insipidus. Previous reported cases of AWI due to desmopressin are discussed. The importance of ruling out primary polydipsia when this drug is used, not only for central diabetes insipidus but also for other current indications such as classic hemophilia, is stressed.