Background: The prevalence of reduced glomerular filtration rate (GFR) in older hypertensive patients and the relationship between level of GFR and cardiovascular disease (CVD) and its risk factors are not well known. Methods: We evaluated baseline renal function in 40514 hypertensive patients 55 years or older who were enrolled in the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT). We used the simplified Modification of Diet in Renal Disease study equation to estimate GFR and examined the prevalence of CVD in patients with different levels of GFR. Results: Fifty-seven percent of patients had mild (60-89 mL/min per 1.73 m2), 17.2% had moderate (30-59 mL/min per 1.73 m2), and 0.6% had severe (≤29 mL/min per 1.73 m2) reductions in GFR. Compared with patients with normal or mildly reduced GFR, patients with moderate or severe reductions in GFR were more likely to have had a prior myocardial infarction or stroke (19.2% and 23.4% vs 28.7% and 26.9%, respectively), have ischemic changes on electrocardiography (ECG) (16.0% and 18.9% vs 24.6% and 34.1%, respectively), and have left ventricular hypertrophy on ECG (ECG-LVH) (3.9% and 4.2% vs 6.0% and 11.2%, respectively). A decrease in GFR of 10 mL/min per 1.73 m2 was independently associated with a 6% higher risk for CVD and 14% higher risk for ECG-LVH. The increase in risk was marked at a GFR of approximately 60 to 70 mL/min per 1.73 m2. Conclusions: The prevalence of reduced GFR is high in older hypertensive patients. Patients with moderate or severe reduction in GFR are more likely to have a history of CVD and ECG-LVH. Even modest reductions in GFR are independently associated with a higher prevalence of CVD and ECG-LVH.