Hypernatremia and polyuria are the main symptoms of diabetes insipidus. Polyuria is characterized by a 24-h urine volume in excess of 40-50 ml/kg in adults. Dexmedetomidine, a highly selective, short-acting intravenous alpha-2 agonist, is used as a component of anesthesia, and has been suspected to induce polyuric syndrome. We report a patient who presented with severe hypernatremia and polyuria after intravenous infusion of dexmedetomidine.