The hepatopulmonary syndrome (HPS) is a functional process and is characterized by the triad of liver cirrhosis, intrapulmonary vascular dilatations, and arterial hypoxemia in absence of detectable intrinsic disease of the lung and the heart. The pathophysiological fundament is the presence of a ventilation-perfusion (VA/Q) inequality based on marked vasodilatation of the pulmonary vessels at the precapillary level. Only in critically ill patients limitations of the diffusion of oxygen from the alveolar gas to the capillary blood and intrapulmonary arteriovenous communications will increasingly contribute to the hypoxemia. For diagnosis of the HPS the arterial blood gases (under condition of room air and 100% oxygen), the contrast echocardiography, the pulmonary angiography, and the multiple inert gas elimination technique will give important informations. Regarding recent studies liver transplantation is the treatment of choice in patients with severe HPS.