The first recorded noise-induced hearing loss was reported by Alberti in 1591. Since Fosbroke reported a survey of hearing loss of factory employees in 1831, a great number of studies have been published in this area. Moreover, in present social development, it has been shown that hearing loss, due to various kinds of noise, is prominent. This is because of the advances in industrial medicine. This has been the cause of one of the medical problems not only in Otolaryngology, but also in society. The main cause of noise-induced hearing loss has been shown to be environmental noise. Also it is related to the duration of exposure, sex and individual susceptibility to such noise. In Korean industry, there has been no adepuate protection against such noise. Therefore, recently, we have noted an increasing tendency for such fearing loss. So it is very important to consider the degree and severity of the noise-induced hearing loss. The author has done a study concentrating on the occurrence, symmetricity, sex difference and degree of such noise-induced hearing loss according to age and years of service. 2235 employees who work in the various kinds of environmental noise at a fabric factory located in Seoul were used as test subjects. The 3 step process in each subject included : 1) Complete case histories in 3 parts : background data (residence, military service), aural history (familial deafness, illness, accidents), and present hearing status (tinnitus, use of telephone). 2) Otological examination 3) Preliminary screening hearing test with a pure tone audiometer on 2000 and 4000 cps over 25 dB. All subjects, following the above 3 step examination, were tested on 8 frequencies with a Beltone Audiometer 15 C which was calibrated by Rudmose RA 106. A testing method used, was a 3 cross testing in 2 ascending and 1 descending trials. The audiological analysis shows the following : 1) The occurrence of noise-induced hearing loss is increased with increasing age and years of service. A closer relation was noted in the male than in female. 2) In both sexes there is a significant change in the direction of poorer hearing with increasing age especially for the higher frequencies. 3) There is a decrease in hearing sensitivity with increasing length of employment in both sexes, but it did not result in a direct proportionate greater loss with greater years of service. 4) Greater hearing losses occur in the left ears than in the right ears above 3000 cps. 5) Greater hearing losses occur in the male than in female above 3000 cps. 6) The pure tone audiogram pattern reveals the dip form, divided dip form, and abrupt form in that order.