Desmopressin diacetate arginine vasopressin (DDAVP) is a synthetic analogue of the mammalian arginine vasopressin used in the treatment of central diabetes insipidus, bleeding disorders, and incontinence. The primary adverse reaction associated with DDAVP is hypotonic hyponatremia. Hyponatremia has been reported in adults treated with DDAVP for Von Willebrand's disease and hemophilia and in children treated for enuresis, but as yet few cases of hyponatremia developing in enuretic adults treated with DDAVP have been reported. We report the cases of two elderly women taking DDAVP for nocturnal polyuria who developed severe hyponatremia. One patient died in the hospital.