BACKGROUND Kawasaki disease (KD) is a systemic vasculitis of childhood with widespread vascular endothelial damage in the acute stage. Long-term complications, such as myocardial infarction and death, are recognized, but the extent and nature of late vascular abnormalities that might predispose to these events have not been studied. RESULTS We used high-resolution ultrasound to study endothelial function in the brachial artery of 20 patients 5 to 17 years after acute KD (median, 11 years) and compared findings with those in 20 age- and sex-matched control subjects. Vascular responses to reactive hyperemia (with flow increase leading to endothelium-dependent dilation) and to sublingual glyceryl trinitrate (GTN; endothelium-independent dilation) were recorded. The relationship between endothelium-dependent vascular responses and features of the endothelium acute illness was examined. There was no difference in baseline vessel diameter, degree of reactive hyperemia, or response to GTN between patients and control subjects. In contrast, flow-mediated dilation was markedly reduced in KD patients compared with control subjects (3.1% versus 9.4%; P < .001). Late endothelium-dependent responses were not related to features of the acute illness. CONCLUSIONS Abnormalities of systemic endothelial function are present many years after resolution of acute KD, even in patients without detectable early coronary artery involvement. Because this may be an important factor in the genesis of late vascular complications, long-term follow-up of all patients with KD is indicated.