It has been well known that several neuropeptides may affect human behavior, and that some endocrinopathies are associated with impaired higher function of the brain. There have been increasing evidences that vasopressin has both peripheral and central effects, the latter of which is involved in memory. In experimental animals, male mice with a null mutation in the V1a receptor (V1aR) exhibit a profound impairment in social recognition and changes in anxiety-like behavior. An AVP fragment analog has been reported to facilitate memory retention and recall in mice through protein kinase C-independent pathways. In human, a few recent reports have suggested that a familial central diabetes insipidus, caused by a heterozygous mutation in the gene for vasopressin prohormone, have minor disturbances in central nervous system. Taken together, it is hypothesized that the subject with central diabetes insipidus may frequently present with an impaired cognitive ability. It is justified to examine the cognitive function, when we make a diagnosis of central diabetes insipidus and to perform a clinical study to investigate whether central diabetes insipidus may be associated with impairment of higher brain functions.