Hyponatremia is defined as a serum below 135 mmol/l and is the most frequent electrolytes disorder. The treatment is essential because hyponatremia is associated with increased morbidity and mortality. There are multiple aetiologies associated with this challenging diagnosis. The correct one must be established in order to manage this disorder appropriately. Serum and urine osmolalities, serum sodium concentration and evaluation of extracellular fluid volume are necessary for the diagnosis. The rate of correction of hyponatremia should be closely monitored to avoid cerebral complications. This article reviews the recommended approaches for the diagnosis and treatment of hyponatremia.