The relationship between the metabolic syndrome and insulin resistance remains controversial, regarding the cause-effect relationship, and the frequency and obligativity of association. Based on these facts and due to the limited possibilities of measuring the decrease of insulin sensitivity in clinical practice, insulin resistance is not included in the criteria recommended by the International Diabetes Federation (IDF) for the diagnosis of the metabolic syndrome. We have investigated the relationship of the metabolic syndrome diagnosed according to this recently introduced system and the reduction of insulin sensitivity estimated by indices calculated from fasting glycemia and insulinemia (HOMA, QUICKI) in 180 persons. Our observations show that modest or moderate decrease of insulin sensitivity is frequently identified in the metabolic syndrome patients. The IDF system may be considered a specific (0,86, CI95%: 0,75-0,94, p<0,001) but less sensitive method for the identification of insulin resistance with a good positive predictive value (0,88, CI95%: 0,78-0,95, p<0,001).