Elevated liver enzymes are a frequent finding in both symptomatic and asymptomatic patients necessitating further evaluation to clarify the underlying disease. Three different patterns of increased liver enzymes can be defined to allow for a more precise and rational further diagnostic approach. A predominant increase in transaminase activities reflects a disturbance of hepatocellular integrity which can be found in patients with viral hepatitis, genetic liver diseases like Wilson`s disease or hemochromatosis, and drug-induced liver diseases. A second pattern is characterized by high serum alkaline phosphatase and γ-glutamyltranspeptidase activities indicating cholestatic liver diseases. The next important diagnostic measure in this group is an ultrasound study discerning intra- from extrahepatic cholestasis. Intrahepatic cholestatic diseases include primary and secondary sclerosing cholangitis, genetic disturbances of canalicular membrane transporters or drug-induced liver dieseases. Extrahepatic cholestasis involves obstruction of the large bile ducts by gall stones or tumors. The third enzym pattern is defined by a predominant rise in γ-glutamyl transpeptidase which is observed in alcoholic or non-alcoholic fatty liver disease and infiltrating liver diseases. A rise in liver enzymes is not necessarily indicative of a primary hepatic origin. Extrahepatic diseases often cause similarly increased serum activities. In addition even higher values can be observed under normal conditions during pregnancy or in adolescens. Lower values in asymptomatic patients should only be controlled since more than 30% of elevated transaminases spontaneously normalize during follow-up.