Abstract—The purpose of this study was to evaluate endothelial function in patients with periodontitis. We evaluated forearm blood flow responses to acetylcholine and sodium nitroprusside in patients with periodontitis who had no other cardiovascular risk factors (32 men; 25±3 years of age), in a normal control group (20 men; 26±3 years of age), and in hypertensive patients with periodontitis (28 men and 10 women; 56±12 years of age) and without periodontitis (control group; 18 men and 6 women; 54±13 years of age). Forearm blood flow was measured using strain-gauge plethysmography. Circulating levels of C-reactive protein and interleukin-6 were significantly higher in the periodontitis group than in the control group. Both in healthy and hypertensive subjects, forearm blood flow responses to acetylcholine were significantly smaller in the periodontitis group than in the control group. Sodium nitroprusside–stimulated vasodilation was similar in the 2 groups. Periodontal therapy reduced serum concentrations of C-reactive protein and interleukin-6 and augmented acetylcholine-induced vasodilation in periodontitis patients with and without hypertension. After administration of N^G-monomethyl-L-arginine, an NO synthase inhibitor, forearm blood flow response to acetylcholine was similar before and after treatment. These findings suggest that periodontitis is associated with endothelial dysfunction in subjects without cardiovascular risk factors, as well as hypertensive patients, through a decrease in NO bioavailability and that systemic inflammation may be, at least in part, a cause of endothelial dysfunction, leading to cardiovascular diseases.