An epidemiologic study of diabetes in the urbanized Polynesian population of Funafuti has established a prevalence of 8 per cent in subjects aged 10 years and over. Of these, only 0.9 per cent were known diabetics, and the remainder were diagnosed on the basis of a plasma glucose level of at least 160 mg/100ml. two hours after a 75 gm. glucose load. A further 5.9 per cent had borderline diabetes as judged by a two-hour postload plasma glucose of 140-159 mg/100 ml. In those aged 20 years and over, the prevalence of diabetes was 10.1 per cent, similar to that reported in other acculturated Polynesian groups. The prevalence of both borderline diabetes and frank diabetes was twice as high in the females as in males. This difference appeared to be related to the greater degree of obesity in the females, but the prevalence was not related to parity. The increase in frequency of diabetes among these islanders coincides with a change of traditional island life style to that of urbanized Western populations. The results suggest that there may be 10 times the actual number of known diabetics in some Pacific populations.