OBJECTIVE - It has been suggested that insulin resistance and consequent hyperinsulinemia promote atherosclerosis, but few prospective studies have reported the relationships between hyperinsulinemia and the development of ST-T abnormalities in the 12-lead resting electrocardiogram (ECG) in populations in which atherosclerosis is rare. RESEARCH DESIGN AND METHODS - A total of 304 Japanese men and women, aged 20-69 years, selected for having high blood glucose or more than a trace-positive urine glucose from a population-based health examination in 1981, were followed for 11 years. Of these, 33 died, 1 from myocardial infarction, while 260/271 living were reexamined in 1992. The 237 subjects with a normal ECG at the baseline examination were analyzed. RESULTS - Incident ST-T abnormalities occurred in 13/237 people. Insulin concentrations were positively associated with the development of ST-T abnormalities (relative risk ~8, comparing those in the highest versus lowest quartile of insulin values). Adjustment for age, sex, and systolic blood pressure or other risk factors had little effect on this relationship. CONCLUSIONS - Hyperinsulinemia was related to the development of ST-T abnormalities in ECGs in the absence of the development of clinical signs of atherosclerosis, independent of blood pressure and other risk factors in men and women with mild glucose intolerance.