Aerobic fitness, resting pulse rate, and self-reported physical activity were examined along with prevalence of cardiovascular disease risk factors in a population-based study of 413 boys and 372 girls, ages 10 to 14 years. Cardiovascular fitness (VO2 max) was predicted from heart rate measured during submaximal bicycle exercise. For both genders, fitness level was significantly and inversely related to body weight, body mass index [weight in kilos/(height in meters)2], triceps skinfold thickness, systolic and diastolic blood pressure, and pulse rate and positively related to high-density lipoprotein/total cholesterol ratio and physical activity. In addition, fitness level was positively related to high-density lipoprotein cholesterol and negatively related to triglycerides in females; it was also negatively related to height, total cholesterol, and hematocrit in males. Analyses of covariance, controlling for sexual maturity ratings, revealed that students in the lowest quartiles of VO2 max had significantly higher body mass index and triceps skinfold thickness than students in the higher quartiles. After adjustment for body mass index and sexual maturity ratings, blood pressure and pulse rate in both genders were significantly higher among students in the lower quartiles of VO2 max than among the groups who scored higher on the fitness test. Higher levels of VO2 max were also associated with a more favorable lipid profile in females. In gender-specific multiple regression analysis, triceps skinfold thickness was the strongest predictor of VO2 max, followed by pulse rate. Our study provides evidence that higher levels of fitness are associated with more favorable risk profiles in adolescents.