BACKGROUND: Endothelial dysfunction has previously been reported in children with a history of Kawasaki disease, but the determinants of endothelial function in Kawasaki disease patients are still unknown. In this study, we investigated endothelial function in Kawasaki disease patients and attempted to identify risk factors for persistent endothelial dysfunction. METHODS: Using high-resolution ultrasound, we measured the percent flow-mediated dilatation, an arterial response to reactive hyperemia, to evaluate endothelial function in 67 patients with a history of Kawasaki disease and 28 age- and sex-matched control subjects. We divided the Kawasaki disease patients into a group with impaired endothelial function (the percent flow-mediated dilatation below -2 standard deviations of the control group) and a group with normal endothelial function (the percent flow-mediated dilatation more than -2 standard deviations of control). Logistic multiple regression analysis was performed to identify independent predictors of impaired endothelial function. RESULTS: In Kawasaki disease patients, the percent flow-mediated dilatation was significantly lower than in the control subjects (9.8±3.6%, compared with 13.1±3.4%, p<0.01). In 13 Kawasaki disease patients (3 patients with coronary artery lesions and 10 patients without coronary artery lesions), the percent flow-mediated dilatation was below -2 standard deviations of control. Logistic multiple regression analysis showed that a febrile period of longer than 10 days during the acute phase was the significant risk factor for endothelial dysfunction (odds ratio: 8.562; 95% confidence interval: 1.366-53.68). Presence of coronary artery lesions was not a determinant of endothelial dysfunction. CONCLUSIONS: Systemic endothelial dysfunction exists in children with a history of Kawasaki disease, and a febrile period of longer than 10 days during the acute phase is an independent predictor of endothelial dysfunction irrespective of coronary artery involvement.