The magnitude and impact of diabetes mellitus as a public health problem on Guam was assessed by retrospective analysis of birth and death certificates, as well as chart review of hospital deaths for complications. Non-insulin-dependent diabetes is common on Guam; insulin-dependent diabetes is rare. Diabetes and diabetes-associated mortality rates were similar to those of the general United States population; however, the age-specific rates in persons aged 45 yr and over were two to three times greater. The mean age of the Guam population is only 18.9 yr, about 10 yr younger than the United States mainland. These circumstances could result in the number of persons aged 45 yr and over increasing disproportionately in the future, increasing dramatically the number of persons at risk to develop non-insulin-dependent diabetes. The population found to have the highest rates for diabetes and related complications was the Chamorros (indigenous Guamanians), who comprise the major population group of the Territory. This population experinced most of the complications associated with diabetes, heart disease and hypertension being important causes of morbidity and mortality on Guam. It is likely that many of the complications of pregnancy associated with diabetes go unrecognized. The cost of diabetes to the Territory was estimated to be at least 3 million dollars per year.