OBJECTIVE - Diabetes and hypertension often co-occur and share risk factors. Hypertension is known to predict diabetes. However, hyperglycemia also may be independently associated with future development of hypertension. We investigated glycated hemoglobin (HbA 1c) as a predictor of incident hypertension. RESEARCH DESIGN AND METHODS - We conducted a prospective analysis of 9,603 middle-aged participants in the Atherosclerosis Risk in Communities Study without hypertension at baseline. Using Cox proportional hazards models, we estimated the association between HbA 1c at baseline and incident hypertension by two definitions 1) self-reported hypertension during a maximum of 18 years of follow-up and 2) measured blood pressure or hypertension medication use at clinic visits for a maximum of 9 years of follow-up. RESULTS - We observed 4,800 self-reported and 1,670 visit-based hypertension cases among those without diagnosed diabetes at baseline. Among those with diagnosed diabetes at baseline, we observed 377 self-reported and 119 visit-based hypertension cases. Higher baseline HbA 1c was associated with an increased risk of hypertension in subjects with and without diabetes. Compared with nondiabetic adults with HbA 1c <5.7%, HbA 1c in the prediabetic range (5.7-6.4%) was independently associated with incident self-reported hypertension (hazard ratio 1.14 [95% CI 1.06-1.23]) and visit-detected hypertension (1.17 [1.03-1.33]). CONCLUSIONS - We observed that individuals with elevated HbA 1c, even without a prior diabetes diagnosis, are at increased risk of hypertension. HbA 1c is a known predictor of incident heart disease and stroke. Our results suggest that the association of HbA 1c with cardiovascular risk may be partially mediated by the development of hypertension.