The structure and function of central arteries are altered with advancing age. These changes comprise arterial dilation, intima-media thickening and increase in stiffness. Arterial wall hypertrophy and increased stiffness are associated with major cardiovascular disease. In contrast to this, physical activity has been found to be inversely related to the incidence of major cardiovascular disease and mortality in humans. However, conflicting data exist on the effect of physical activity on arterial stiffness and very little data about its association with structural arterial properties. We therefore investigated the association of the self-selected leisure-time physical activity (LTPA), assessed by a self-administered questionnaire, with the structure and function of the common carotid artery, examined with high-resolution ultrasound, in 51 male subjects aged between 16 and 78 years. We found that men with a higher level of LTPA (> 38.1 MET*h/week = H-LTPA) (metabolic equivalent value; 1 MET= energy expended by a person at rest, i.e. approximately 3.5 ml oxygen uptake/kg body mass or 1 kcal/kg per h) had a significantly lower arterial stiffness (P = 0.02) than men with lower levels ( < 38.1 MET*h/week = L-LTPA) (4.32+/-1.17 versus 5.75+/-1.21 x 10(6) cm(-2)). In multiple regression analyses, with several atherosclerotic risk factors as correlating variables with arterial stiffness, LTPA persisted as an independent predictor of arterial stiffness (adjusted R2=0.19) in addition to apolipoprotein B level (adjusted R2 = 0.33). The study could not, however, show an association of LTPA with reduced intima-media thickness (L-LTPA = 0.66+/-0.15 versus H-LTPA 0.66+/-0.14) or arterial dilation of diastolic diameter (L-LTPA = 6.34 + 0.64 versus H-LTPA 6.08+/-0.69). However, the positive association of LTPA with several parameters, which correlated inversely with intima-media thickness, may be taken as an indicator for a possible positive (not visible in an ultrasonic examination of the common carotid artery) effect of LTPA on the arterial wall structure.