Physicians sooner or later discover, through clinical experience, the need for special competence in assessing the mental faculties of their patients. They must be able to observe with objectivity the patient’s attention, intelligence, memory, judgment, mood, character, and other attributes of cognitive performance, and personality in much the same fashion as they observe the patient’s movements, gait, and reflexes. The systematic examination of these intellectual and affective functions permits the physician to reach conclusions regarding the patient’s mental status and its relationship to his illness. Without such data, there are likely to be errors in the diagnosis and treatment of the patient’s neurologic, general medical, and psychiatric disease.