The frequency of auditory exostoses was examined by latitude. It was found that discrete bony lesions of the external auditory canal were, with very few exceptions, either absent or in very low frequency (less than 3.0%) in 0-30 degrees N and S latitudes and above 45 degrees N. The highest frequencies of auditory exostoses were found in the middle latitudes (30-45 degrees N and S) among populations who exploit either marine or fresh water resources. Clinical and experimental data are discussed, and these data are found to support strongly the hypothesis that there is a causative relationship between the formation of auditory exostoses and exploitation of resources in cold water, particularly through diving. It is therefore suggested that since auditory exostoses are behavioral rather than genetic in etiology, they should not be included in estimates of population distance based on nonmetric variables.