The hepatopulmonary syndrome is characterized by the combination of hypoxemia and endopulmonary vascular dilatations in patients with liver disease. Its prevalence ranges from 4% to 29%. Pathology tissue examination reveals dilated arterioles and capillaries as well as communications between arteries and veins. Evidence exists that endopulmonary dilatations correlate with the presence of portal hypertension. The increased production of nitrogen monoxide (NO) and the activation of endothelin receptors are shown to play an important role in the pathogenesis of the syndrome by causing vascular dilatation and by interrupting the normal mechanism of hypoxic vasoconstriction in the lung. Hypoxemia is found in the majority of patients with hepatopulmonary syndrome. In severe cases the phenomena of orthodeoxia and platypnoea ensue. The documentation of endopulmonary dilatations is based on three methods: a. contrast echocardiography, b. perfusion radionuclide scanning with 99mTc, c. pulmonary angiography. Treatment includes oxygen therapy, correction of portal hypertension and in specific cases liver transplantation. Prognosis is poor and mortality exceeds 40%. Pneumon 2006, 19(1):36-41.