A diabetes prevalence study on an isolated urbanized Central Pacific Island has established a prevalence rate of 34.4% in individuals aged 15 years and over. Of these, 10.4% had previously known diabetes; in the others the diagnosis was made on the basis of a plasma glucose level of at least 160 mg/100 ml 2h after a 75 gm oral glucose load. A further 11.3% of the subjects had borderline diabetes as judged by a 2-h plasma glucose of between 140 and 159 mg/100 ml. Of the diabetics, 72% had a positive family history of diabetes. The high prevalence rate appears to be related to a number of factors including a diabetic genotype, urbanization, and obesity.