Kawasaki disease (KD) is an acute febrile vasculitic syndrome of unknown etiology that preferentially affects the coronary artery. Interleukin-10 (IL-10) is a key proinflammatory cytokine, and a polymorphism near the major transcriptional start site of the IL-10 gene was shown to influence IL-10 production in vitro. This study investigated the association of the IL-10 promoter polymorphism with KD and its clinical parameters in Korean children. A total of 194 children with congenital heart disease (CHD) and 95 children with KD were included in this study. IL-10 (-627 A/C) polymorphism genotypes were determined using the single-base extension method. There was no difference in the allele frequencies of IL-10 (-627 A/C) polymorphism between CHD children and KD children. KD children with one or two copies of the IL-10 (-627C) allele showed significantly lower albumin levels (p ϭ 0.020) and higher frequencies of early coronary artery aneurysm [62.22% versus 37.78%, adjusted odds ratio (aOR) ϭ 3.50, 95% confidence interval (CI): 1.50 -8.16] compared with KD children with the common IL-10 (-627A) allele. These findings suggest that the IL-10 (-627 A/C) promoter polymorphism might be a genetic marker for the risk of early coronary artery complication in KD. (Pediatr Res 61: 584-587, 2007) K D is an acute, self-limiting vasculitis of unknown etiology that occurs predominantly in infants and young children. KD is characterized by widespread vascular inflammation of the coronary artery and other medium-sized arteries (1,2). Coronary artery lesions, including coronary artery dilatation or aneurysm, are the most common complications and develop in approximately 20%-25% of untreated children with KD (3). Even after high-dose intravenous immunoglobulin (IVIG) therapy, coronary artery lesions occur in a small percentage of KD patients, occasionally leading to lifethreatening complications (e.g. myocardial infarction) and/or acquired heart diseases such as myocardial dysfunction, valvular diseases, and arrhythmias (4,5).