High Quality Content by WIKIPEDIA articles! The International Classification of Diseases (most commonly known by the abbreviation ICD) is according to its publisher, the United Nations-sponsored World Health Organization "the standard diagnostic tool for epidemiology, health management and clinical purposes." It is known as a health care classification system that provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. Under this system, every health condition can be assigned to a unique category and given a code, up to six characters long. Such categories can include a set of similar diseases.