This Finnish population-based study, mean age 46 years, evaluates the association of high-sensitivity C-reactive protein (hs-CRP), interleukin-1 receptor antagonist (IL-1Ra), and adiponectin with the NCEP and IDF definitions of metabolic syndrome (MetS). Adiponectin levels were higher, hs-CRP and IL-1Ra levels lower in subjects without MetS compared to subjects with MetS. If MetS was present according to both IDF and NCEP criteria, BMI, waist, triglycerides, hs-CRP, and IL-1Ra were significantly higher compared to subjects who had MetS according to either only IDF or only NCEP criteria. The hs-CRP, IL-1Ra, and adiponectin linearly correlated with the number of the components of MetS according to both definitions. Decreased levels of adiponectin and increased levels of hs-CRP and IL-1Ra are tightly associated with the components of MetS. Individuals who had MetS according to both criteria had the most adverse changes in cardiovascular risk factors.