Anorexia nervosa (AN) resembles the 'great pretenders' of medicine in the nineteenth century, syphilis and tuberculosis, by presenting occultly as a disorder of specific organs. Many physicians fail to identify the true primary cause, AN, which can mimic in its medical consequences gastrointestinal disorders, endocrine failure, pituitary tumors, or cancer. This is especially likely when the patients are older, have an established complex medical history, and challenge a specialist to find a medical cause and treatment, resulting in ordering more laboratory tests and medical instrumentation. Everyone suffers as a result, including the patient, the family, the frustrated physician, and the National Health Service, for whom the costs of medical care of these patients are enormous and out of proportion. Remembering that AN is as much a medical as a psychological disorder, assessing the patient with more time and expertise in history taking, and referring to a psychiatric consultant when National Institute for Clinical Excellence guidelines for identifying AN in non-mental health settings trigger suspicions, results in good outcome of the AN, cessation of ineffective gastrointestinal treatments, and substantial savings to the National Health Service. (C) 2004 Lippincott Williams Wilkins.