The association between cardiorespiratory fitness (VO2max) and carotid atherosclerosis was analyzed in 163 men, aged 50 to 60 years. VO2max was assessed using breath-by-breath respiratory gas analyses during maximal exercise stress test. Atherosclerosis was evaluated quantitatively as intima-media thickness (IMT) of the right and left carotid arteries by high-resolution B-mode ultrasonography. Mean VO2max was 29.6 ml/kg per min (95%CI 28.7;30.5), common carotid IMT 1.04 mm (95%CI 1.01;1.07) and carotid bifurcation IMT 1.73 mm (95%CI 1.66;1.81). VO2max correlated inversely with carotid bifurcation IMT (r = -0.31, P < 0.001), but not with common carotid IMT (r = -0.13, P = 0.102). Men in the highest quartile of VO2max had lower (P < 0.001) bifurcation IMT 1.51 mm (95%CI 1.41;1.61) than men in the lowest (1.95 mm (95%CI 1.75;2.16)) and in the second lowest VO2max quartile (1.79 mm (1.63; 1.95)). The difference persisted (P = 0.014) after controlling for age, LDL-cholesterol, systolic blood pressure, saturated fat intake, current health status and exercise-induced ST-segment depression. These data suggest that cardiorespiratory fitness is an important independent predictor of carotid atherosclerosis in middle-aged men.