The pattern of uveitis seen in a caucasian population in Iowa was found to be very similar to that seen in London in spite of geographical and climatic differences in the two locations. Acute anterior uveitis was the commonest type of uveitis but fewer of the Iowa patients showed radiological evidence of ankylosing spondylitis or Reiter's syndrome. Toxoplasmosis was responsible for 9% of cases in both series. It is concluded that genetic factors are more important than geographic location in determining the types of uveitis which occur in a caucasian population.