Worldwide diabetes epidemiology studies have shown quite marked differences in diabetes prevalence rates between ethnic groups. This pattern holds true in the Pacific region and provides unique opportunities for comparative studies. Diabetes is rare in Melanesians, and also in Polynesians, Micronesians, and Australian Aboriginals who retain their traditional life-style. High prevalence rates of insulin-independent diabetes have been demonstrated in Polynesians, Micronesians, and Australian aboriginals who have adopted a Western life-style. Along with the Pima Indians, the Micronesian population of Nauru have the highest diabetes prevalence yet reported, 40% of people aged 20 yr and over. As diabetes is rare in traditional living Polynesians and Micronesians, yet high in westernized populations of these ethnic groups, it appears these people may have a 'diabetic genotype' that is unmasked by the change in life-style. Obesity, a high caloric Western diet, and reduced physical activity may be the major precipitating factors. Bimodality of glucose tolerance distributions has been demonstrated in both westernized Polynesians and Micronesians. The frequency distributions of both fasting and 2-hr postload glucose levels allow separation of these populations into normal and hyperglycemic groups. The optimal cut-off levels between the two groups were a fasting plasma glucose ≃140 mg/dl and a 2-hr level of ≃200 mg/dl. These findings provide a valid basis for the diagnosis of diabetes mellitus to be based on the above levels. Only sparse information exists on the prevalence of microvascular and macrovascular complications of diabetes in these populations. However, there is clear evidence that they are occurring and they are similar in nature to the complications seen in Caucasian diabetic patients. Coronary artery disease is not yet a major problem in Pacific Islanders although most of the major risk factors are not present in urbanized communities. However, with increasing westernization, and given more time for the pathologic process of atheroma to develop, it can be expected that coronary artery disease will become a major cause of morbidity and mortality in Polynesians, Micronesians, and the Australian aboriginal.