Hepatorenal syndrome is a common complication in patients with advanced cirrhosis and ascites characterized not only by renal failure but also by marked alterations in systemic hemodynamics and vasoactive systems. Renal failure is due to a marked hypoperfusion of the kidney secondary to renal vasoconstriction. The pathogenesis of hepatorenal syndrome is not completely known but it is thought to be the extreme manifestation of the underfilling of the arterial circulation secondary to an arterial vasodilation, located mainly in the splanchnic circulation. Recently, a new definition and diagnostic criteria of hepatorenal syndrome have been proposed, which has stimulated research in this field. Prognosis of patients with hepatorenal syndrome is very poor. Liver transplantation is the only effective treatment but it is not applicable in all patients due to short survival. New therapies developed during the last few years, such as the use of systemic vasoconstrictors or transjugular intrahepatic portosystemic shunts appear promising, but their usefulness should be evaluated in prospective investigations.