Exostosis of the external ear canal is a disease unique to man. It has been identified in prehistoric man, affecting the aborigines of the North American continent. Aural exostoses are typically firm, sessile, multinodular bony masses which arise from the tympanic ring of the bony portion of the external auditory canal. These growths develop subsequent to prolonged irritation of the canal. The large, primitive jaw of prehistoric man placed great mechanical stress on the tympanic ring. Chronic aural suppuration seen in the preantibiotic era was soon followed by exostoses. Today, prolonged contact of the external ear canal with cold sea water is the most prevalent cause (aquatic theory). As a result the disease is now essentially limited to coastal regions. In this way we have seen exostoses appear in different stages of the evolution of man as a result of mechanical, chemical and now thermal irritation. The author is an otolaryngologist in a coastal region. In examining 11,000 patients during a ten-year period, 70 cases of symptomatic exostoses of the external auditory canal were identified. The incidence of exostoses was found to be 6.36 per 1,000 patients examined for otolaryngologic disease. It is a predominantly male disease. The development of these "irritation nodules" is painless until the tenth year of aquatic exposure to irritation, when symptoms of obstruction occur. The hearing loss associated with exostoses is usually a conductive type, secondary to occlusion of the canal by impacted cerumen or acute external otitis. The results of studying the thermal characteristics of the body of water used for such aquatic activities is presented.