The aim of this epidemiological study is to characterize the neuropsychological and motoric performance in patients with hyponatremia. Newer studies revealed an association between mild hyponatremia and unstable walking, frequency of falls and risk of a fracture, questioning the paradigm of an "asymptomatic" hyponatremia. Until now, there is no known detailed investigation and characterisation of the cognitive and motoric performance or limitation by this disorder. Therefore this study will investigate patients with hyponatremia on the basis of neuropsychological and neurological tests.