OBJECTIVE - Glycemic control (HbA1c [A1C]) is strongly associated with microvascular disease in individuals with diabetes, but its relation to macrovascular disease and atherosclerosis is less clear. This study examines the relationship between A1C, carotid intima-media thickness (IMT), and traditional cardiovascular risk factors in individuals with diabetes. RESEARCH DESIGN AND METHODS - A cross-sectional study of 2,060 people with diagnosed and undiagnosed (unrecognized) diabetes in the Atherosclerosis Risk in Communities study was performed. RESULTS - LDL and HDL cholesterol, plasma triglycerides, and waist-to-hip ratio were significantly associated with A1C after multivariable adjustment. African Americans with undiagnosed and diagnosed diabetes had significantly elevated A1C values compared with whites, even after adjustment for potentially confounding factors. There was a graded association between A1C and carotid IMT. In a fully adjusted model in individuals with undiagnosed diabetes, the odds ratio (OR) of being in the highest quartile of IMT versus the lowest was 2.46 (95% CI 1.16-5.03, comparing the highest quartile of A1C to the lowest). In people with diagnosed diabetes, the comparable OR was 2.62 (1.36-5.06). CONCLUSIONS - This study identified several important associations between A1C and known risk factors for cardiovascular disease and suggested that A1C is independently related to carotid IMT. Chronically elevated glucose levels may contribute to the development of atherosclerosis in people with diabetes, independent of other risk factors.