Patients usually go to doctors with symptoms, not with the names of diseases or conditions. The doctor’s task is to make sense of the patient’s complaints within the framework of medical diagnoses and recognized diseases. But many patients have symptoms that remain unexplained after the diagnostic process is exhausted. This is the case because modern medicine focuses on diseases that have a basis in the structure or anatomy of the body systems rather than functional disorders that have a basis in how the systems work. In effect, symptoms remain “unexplained” not because they cannot be explained but because some doctors do not know how to explain them. Revised and updated 2009.