This paper assessed 300 surfboard riders, comprising 229 males and 71 females to determine the prevalence and rate of growth of exostoses in this population. A group of cold water swimmers and a control group were also examined. Significant obstruction, defined as two thirds or more occlusion of the ear canal was noted in 90 of the male surfers and 10 female surfers. This degree of occlusion was found in seven of the 32 cold water swimmers. A male surfer who has surfed regularly for 20 years or more has a one in two chance of developing significant obstruction of the external ear canal resulting from exostoses and this is a three in seven chance for females.