Hyponatremia is a frequent complication of the advanced liver disease, being, as the hepatorenal syndrome, a consequence of the important circulatory dysfunction of cirrhosis. Hyponatremia is determined by the impaired capacity of the kidney to excrete free water, which leads to water retention disproportionate to sodium retention, thus causing low plasma osmolarity. Hyponatremia in cirrhosis is associated with a high morbidity and mortality, its presence suggesting a very advanced liver disease. Current evidence suggests that hyponatremia affects the brain function and predisposes to hepatic encephalopathy. In addition, hyponatremia is a risk factor for liver transplantation, being associated with a high frequency of complication and affecting short and long-term post-transplant survival.