BACKGROUND: The purpose of this cross-sectional study was to examine the impact of below-average cardiovascular fitness and inactivity on the metabolic syndrome among an understudied population-undergraduate men and women, ages 18-24 years. METHODS: Between January, 2010, and May, 2012, we assessed anthropometric, biochemical, and clinical measures in a convenience sample of students (n=1610) enrolled in an introductory nutrition course at a public university. We quantified the prevalence of metabolic syndrome criteria, estimated cardiovascular fitness via a 1-mile Rockport Walk Test, and evaluated daily activity via pedometer. Subjects were classified as below-average, average, and above-average fitness based upon the Rockport Walk Test; activity levels were classified as low active, somewhat active, active, or highly active according to average steps per day. RESULTS: Those with below-average fitness (10%) were at increased risk for being overfat, having abdominal obesity, and having the metabolic syndrome as compared to those with average or above-average fitness (odds ratio: 12.4, 10.0, and 4.7, respectively; all P<0.01). Twenty percent of subjects were low active (<7500 steps/day) and had a greater number of metabolic syndrome criteria as compared to very active subjects (>12,500 steps/day) (0.94±0.05 vs. 0.73±0.05, P=0.01). CONCLUSIONS: Young, college-age adults with below-average cardiovascular fitness and/or low activity levels are at increased risk for obesity and the metabolic syndrome. Future studies should examine how promoting lifestyle habits that increase physical activity and reduce sedentary behaviors during the young adult years can improve metabolic health.