The purpose of this study was to investigate the process of changes in hearing of pure tones with aging. Among individuals who had undergone thorough medical examination for the purpose of annual health-checks, 293 males (586 ears) whose hearing level had been examined for five years or more were enrolled in this study. Cases having conductive deafness or known sensori-neural deafness were excluded. Since the most typical change with aging is observed at 8 kHz, the investigation was carried out only on hearing at 8 kHz. Hearing level increasingly declined with advancing age. Hearing distribution for young subjects showed a peak in the normal hearing level range. This peak decreased with aging, and another peak appeared at 50 dB. Investigation of differences in hearing in the individuals over the five years showed that most subjects had a hearing level difference of 0 dB up to 54 years of age. From 55 years old onward, however, the difference was 5 dB. This indicates that gradual deterioration of hearing level with aging occurs most frequently. On the other hand, in some subjects, deafness progressed faster. Thirty-four and a half percent of the subjects had deteriorations of 20 dB or more in a single year during the entire observation period. A deterioration of 20 dB or more was noted in 4% of the young and 8% of the elderly. Such rapid progression of deafness was believed to be involved in formation of the 50 dB peak in the hearing distribution.