The term diagnosis comes from the Greek gnosis , meaning knowledge. It is the process of determining the nature of a disease or disorder and distinguishing it from other possible conditions. The diagnostic process is the method by which health professionals select one disease over another, identifying one as the most likely cause of a person's symptoms. Reaching an accurate conclusion depends on the timing and the sequence of the symptoms, past medical history ( PMH), risk factors" for certain diseases, and a recent exposure to disease. The physician, in making a diagnosis, also relies on various other clues such as physical signs, nonverbal signals of distress, and the results of selected laboratory and radiological and other imaging tests. From the large number of facts obtained, a list of possible diagnoses can be determined, which are referred to as the differential diagnosis". MEDICAL HISTORY The medical history of a patient is the most useful and important element in making an accurate diagnosis, much more valuable than either physical examinations or diagnostic tests. The medical interview is the process of gathering data that will lead to an understanding of the disease and the underlying physiological process. A complete medical history consists of an account of: (1) the present illness, (2) past medical history,(3) family history (4 ) occupational background (5) psychosocial history, and (6) a review of body systems.