Our hypotheses were confirmed: The fastest hearing deterioration occurred for new tinnitus cases. A moderate genetic influence for tinnitus was confirmed.

Genetic factors are of considerable importance for level of hearing acuity, but environmental factors are more important for rate of change over an 18-year period.

Pre-existing hearing loss can increase the risk of hearing impairment due to occupational noise exposure. An increased risk for NIHL was also seen in the group with exposures below 85 dB(A), a result that indicates awareness of NIHL should be raised even for those working in environments where sound levels are below 85 dB(A).