A population-based survey of 2938 subjects has demonstrated a high prevalence of non-insulin-dependent diabetes (NIDDM) in the Micronesian population of Kiribati (formerly the Gilbert Islands). This finding provides further support for evidence from Nauru, Guam, and the Marshall Islands that Micronesians are particularly susceptible to NIDDM. The age-standardized prevalence was over twice as high in an urban, as compared with a rural, sample (9.1 versus 3.0 in men, 8.7 versus 3.3 in women). To test the a priori hypotheses that obesity, reduced physical activity, and a nontraditional diet are associated with NIDDM, indices of these factors were compared in rural and urban subjects. The rural population was found to be leaner, to have a higher estimate of habitual physical activity, and to have a lower percentage of daily energy intake derived from imported foods. Further analysis demonstrated that obesity alone was insufficient to explain the rural-urban difference in prevalence of NIDDM. The multiple logistic regression model demonstrated a significant association between the prevalence of NIDDM and both obesity and urbanization in men. In women, obesity, physical inactivity, and urbanization were all associated with increased prevalence of NIDDM.