In cases of noise induced hearing loss, the medicolegal judgement of causality often is complicated by the coincidence of endogenous hearing impairments, which conceal the audiological characteristis and the degree of Nihl. The recognition of an occupational disease however is possible only when there is a dominant probability; the possibility of Nihl alone in sight of the labour conditions is not sufficient for this recognition. In such cases, the medical expert therefore, besides of an extensive audiological analysis, must have sufficient information on noise immission, on the course of hearing impairment in regard to working time, and on other diseases and accidents which possibly can influence hearing function.