Psychogenic polydipsia is an uncommon clinical disorder characterized by excessive water-drinking in the absence of a physiologic stimulus to drink. The excessive water-drinking is well tolerated unless hyponatremia supervenes. The diagnosis of psychogenic polydipsia is one of exclusion and requires specialist investigation and management; the most important test is the water deprivation test, which should be undertaken carefully. Water intoxication has occurred in a case administered desmopressin treatment without water deprivation test. The importance of differential diagnosis in polydipsia is emphasized. Anahtar Kelimeler : psikojenik, polidipsi, antidiüretik hormon, psychogenic, polydipsia, antidiuretic hormone