The diagnosis of IE is often difficult to establish with certainty. Current diagnostic criteria have several weaknesses, the most important being failure to utilize the results of echocardiography. This seems inconsistent with modern practice. In reality, the results of modern echocardiography, including appropriate use of transesophageal echocardiography, are critically important for diagnosis of infective endocarditis. New criteria are in the process of development which should prove more sensitive and more specific for disease classification, epidemiologic studies, and clinical trials.