The vascular endothelium is not only a semi-permeable barrier between the blood and the interstitium but also a homeostatic organ with physiological, biological, and endocrine functions. In adults, several studies have investigated the peripheral circulation using the forearm hyperemic response in patient with risk factors for atherosclerosis [13–16]. These studies have demonstrated that peripheral vascular endothelial function plays a crucial role in preventing the progression to coronary arteriosclerosis. However, in children, there have been only a few clinical reports of endothelial dysfunction following vasculitis such as Kawasaki disease as well as following other inflammatory disease such as SLE and JIA [17, 18].