Diabetes insipidus is a rare complication after carbon monoxide poisoning. We report on a woman and her daughter who were noted to have polyuria and hypernatremia after exposure to carbon monoxide. Both patients were responsive to desmopressin therapy, and the diagnosis of central diabetes insipidus was made. The development and correction of hypernatremia further complicated the neurological damages caused by carbon monoxide poisoning. These cases illustrate the possibility of central diabetes insipidus and hypernatremia after carbon monoxide poisoning and the importance of immediate antidiuretic hormone treatment and careful fluid therapy.