OBJECTIVE Diabetes is a major risk factor for morbidity and mortality from cardiovascular disease. However, the role of the primary metabolic abnormality of diabetes (chronic hyperglycemia) in this disease process has not been fully elucidated. METHODS A cross-sectional analysis was conducted among 489 persons with non-insulin-dependent diabetes mellitus; 299 were established diabetics (diagnosed previously) and 190 were newly diagnosed at the time of the Insulin Resistance Atherosclerosis Study (IRAS) examination. These men and women, of three different ethnic groups, were participants in IRAS. Established diabetes (versus newly diagnosed diabetes) and mean fasting glucose level were used as measures of hyperglycemic burden. Intimal-medial wall thickness (IMT) of the internal (ICA) and common (CCA) carotid arteries were used as indices of atherosclerosis. RESULTS The mean duration of disease among established diabetics was 7 years. The mean CCA IMT and ICA IMT were 872 and 946 microns, respectively. Established diabetes and mean fasting glucose level were positively associated with increased CCA IMT (P < .05) but not ICA IMT, even after adjustment for numerous cardiovascular disease risk factors. CCA IMT was increased by 70 microns in established diabetics (versus newly diagnosed diabetics) and by 26 microns per 1 SD of fasting glucose. Among established diabetics, however, duration of known diabetes (number of years) was not significantly related to IMT. CONCLUSIONS Among diabetics in IRAS, established diabetes and fasting glucose level were each independently associated with CCA IMT, suggesting that chronic hyperglycemia or its associated metabolic abnormalities may lead to increased risk of atherosclerosis.