Nontraditional atherosclerotic risk factors have become the focus of attention in recent years. In addition, metabolic syndrome is gaining recognition as another multiplex cardiovascular risk factor. However, to date, no studies have investigated the effect of metabolic syndrome on circulating soluble CD40 ligand (sCD40L), monocyte chemoattractant protein 1, cellular adhesion molecules, and disease severity in patients with symptomatic coronary artery diseases. This study was conducted to address this issue. Patients with stable angina who received percutaneous coronary interventions for significant (> or = 70% diameter stenosis) de novo lesions between January 1999 and January 2004 and had preprocedural serum samples were enrolled. Metabolic syndrome was defined by the National Cholesterol Education Program criteria with waist criterion modified into body mass index of more than 25 kg/m2. The serum samples were thawed and analyzed for circulating sCD40L, monocyte chemoattractant protein 1, adhesion molecules, and high sensitivity C-reactive protein (hs-CRP). Coronary severity was assessed by a modified version of Gensini scoring system. A total of 313 patients, 248 males and 65 females, were studied. Among them, 222 (70.9%, 170 males and 52 females) had metabolic syndrome. Patients with metabolic syndrome had higher serum creatinine level and lower low-density lipoprotein cholesterol despite higher triglyceride concentration. In multivariate analysis, patients with metabolic syndrome had higher sCD40L (6057 +/- 275 vs. 5051 +/- 423 pg/mL, P = .037) and more hs-CRP in higher tertiles (P = .005) than patients without, but similar levels of intercellular adhesion molecule 1, vascular cell adhesion molecule 1, and P selectin. Metabolic syndrome was also significantly associated with multiple coronary vessel involvements with 70% or higher diameter stenosis (36.5% double-vessel and 14% triple-vessel diseases vs 30.8% double-vessel and 5.5% triple-vessel diseases, P = .026) and multiple coronary segment involvements with 50% or higher diameter stenosis (P = .014) in multivariate analysis. In conclusion, the presence of metabolic syndrome is independently associated with elevated sCD40L, hs-CRP, and coronary disease severity in patients with coronary artery disease requiring interventional treatment of stable angina.