Sudden deafness (SD) is a sensorineural hearing loss with an abrupt onset and of unknown origin. SD was designated as a specific disease by the Ministry of Health and Welfare of Japan in 1973. Since then, studies on SD have rapidly advanced. SD is particularly noted as one of the most remarkable sensorineral hearing loss, because of hearing recovery in earlier stage. Present study was conducted to clarify nationwide epidemiol gical surveys, treatments and prognosis.