Increasing physical activity is recommended as a therapeutic lifestyle change in the treatment of metabolic syndrome (MetS); however, little evidence exists for a relationship between cardiorespiratory fitness (CRF) and MetS in representative samples. Using data from the US National Health and Nutrition Examination Survey, 1999-2002, the relationship between CRF and MetS was examined in 692 men and 608 women between the ages of 18 and 49 y who were free of major disease and disability. In men, the odds of MetS were significantly lower in moderate and high CRF categories versus the low CRF category, whereas in women there were no significant relationships between CRF and MetS.