Hyponatremia is the electrolytic disorder that is observed most frequently in hospitalized patients. Itinfluences prognosis in the short, mid and long term. Although many cases are asymptomatic, hyponatremia can cause severe neurological symptoms, depending on the amount of serum sodium reduction and on the rapidity with which it occurs. Thus, treatment assumes crucial importance and must be accompanied by careful monitoring of urine output and serum sodium to prevent accelerated corrections and therefore the risk of osmotic demyelination syndrome. The various therapies have different indications according to the underlying cause of hyponatremia, the presence and severity of symptoms, the duration and degree of the electrolytic alteration. Over the last few years, the aquaretic agents and in particular tolvaptan have acquired great importance compared with the traditional therapeutic approaches (fluid restriction, 3% saline solution and, more rarely, demeclocycline, lithium and urea). In Europe, the oral tolvaptan has been commercialized only for the treatment of euvolemic hyponatremia due to SIADH (syndrome of inappropriate secretion of antidiuretic hormone).Conversely in the USA, intravenous conivaptan (V1a/V2 vasopressin receptor antagonist) and oral tolvaptan have been marketed for the treatment of both euvolemic and hypervolemic hyponatremia.Besides being effective drugs, aquaretics have the benefit of having drawn the attention of physicians against hyponatremia. Unlike infusion saline therapy or fluid restriction, aquaretics allow them to establish long-term therapies which, once started in a hospital setting for safety reasons, may be continued at the patient's home, still under close monitoring.