The clinical syndrome of portal-systemic encephalopathy is caused by far advanced cirrhosis of the liver in most cases; it is characterized by increasing drowsiness, disturbances of mentation, flapping tremor and hyperreflexia. An early diagnosis can be established by testing writing and drawing abilities. Increased occurrence of spider nevi, a dry, deep red tongue, and hemorrhagic lesions of skin and mucous membranes are symptoms of incipient hepatic insufficiency. The syndrome is initiated in most cases by excessive intake of protein or alcohol, by intestinal bleeding, by diuretics, or by intercurrent infections. Therapy has to include elimination of causes, reduced intake of protein, enemas with acetate buffer solution and oral medication with lactulose, bifidum milk, and certain amino acids in order to lower hyperammoniemia; in serious cases neomycin has to be given. At the same time a normalization of fluid and electrolyte balance has to be achieved; replacement of potassium is especially important, when hypokalemia and alcalosis are present. In general prognosis of portal-systemic encephalopathy however is serious, depending primarily upon the fact, whether or not sufficient functional hepatic parenchyma is present.