Water homeostasis in the body is finely balanced by the release of the antidiuretic hormone vasopressin and the stimulation of thirst. Vasopressin acts in the kidneys to concentrate urine and reduce plasma osmolality. Diabetes insipidus is a disorder of water balance characterized by a failure to concentrate urine. There are two types of diabetes insipidus: central and nephrogenic. Central diabetes insipidus is caused by insufficient production of vasopressin, while nephrogenic diabetes insipidus is caused by an impaired response of the kidneys to vasopressin. Patients with central diabetes insipidus respond to treatment with vasopressin or its synthetic analogue, desmopressin; however, caution should be utilized in treating infants with vasopressin or analogues-infants can be treated successfully with fluids alone. Treatment of nephrogenic diabetes insipidus involves removing the underlying cause, if possible, reducing solute load or therapy with a diuretic agent.