Liver diseases are common, and currently represent the 12th leading cause of death in the United States. However, numerous hepatic disorders exist, and differential diagnosis often is difficult. Moreover, because laboratory testing is routine, an abnormal serum transaminase or alkaline phosphatase in patients without clinical symptoms is not uncommon. Although liver function tests are critical in recognizing the presence of liver disease and its specific diagnosis, the interpretation of the tests may be confusing and difficult. Furthermore, not all persons with one or more test abnormalities actually have liver disease. In this review, liver function tests and an approach to their interpretation are discussed.