The International Diabetes Federation (IDF) proposed a new definition for metabolic syndrome (MS) in 2005. We conducted this study to compare the association of MS by IDF and ATP III definition to various metabolic variables. In 2005, we enrolled 654 Chinese people in a screening program in Taiwan. Anthropometric and biochemical profiles, including high-sensitivity C-reactive protein (hsCRP), were measured. Serum hsCRP levels were higher in those with MS by IDF definition (2.4+/-1.9mg/l versus 1.3+/-1.4mg/l, p<0.0001). Serum hsCRP levels increase with the number of components of MS they met (p for trend<0.001). Serum LDL levels were higher in those with MS by IDF definition (131+/-39 versus 125+/-32, p<0.05) but not in those with MS by ATP III definition (p=0.2). Serum hsCRP levels correlate significantly to MS by ATP III definition, after adjusting for age, sex, smoking, body mass index, serum apolipoprotein A1 and LDL levels. Adding MS status by IDF definition in this model significantly increased model fitness in men (MS by IDF definition, partial r=0.18, p<0.05, MS by ATP III definition, partial r=0.12, p=0.071). In conclusion, IDF definition of MS has a stronger relationship with serum hsCRP than ATP III definition in men.