The association between the severity of coronary artery disease (CAD) and metabolic syndrome (MS) as defined by recently proposed criteria remains unknown. Therefore, we investigated the association between the severity of CAD and MS based on four sets of criteria. The frequency of MS and the severity of CAD determined using the Gensini score (GS) were assessed in 656 consecutive patients who underwent elective coronary angiography for the first time. Using the various criteria, 25.4% of males and 25.6% of females fulfilled the NCEP-ATPIII criteria, 46.6% of males and 21.3% of females fulfilled the International Diabetes Federation (IDF) criteria, 44.0% of males and 41.9% of females fulfilled the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) criteria, and 42.5% of males and 18.8% of females fulfilled the Japanese definition. On multivariate analysis, MS defined according to the AHA/NHLBI criteria was related to an increased risk of extensive CAD in males [odds ratio (OR) 1.89, p=0.001]. MS defined according to the IDF criteria was associated with the highest risk for extensive CAD in females (OR 2.83, p=0.019). In conclusion, MS was found to be associated with the extent of CAD. However, gender-specific differences and MS definition-specific differences exist.