Background - The burden of atherosclerosis especially afflicts the increasing older segment of the population. Recent evidence has emphasized a protective role of endogenous sex hormones in the development of atherosclerosis in aging men. Methods and Results - We studied the association between endogenous sex hormones and progression of atherosclerosis in 195 independently living elderly men. Participants underwent measurements of carotid intima-media thickness (IMT) at baseline in 1996 and again in 2000. At baseline, serum concentrations of testosterone ( total and free) and estradiol ( total and free E-2) were measured. Serum free testosterone concentrations were inversely related to the mean progression of IMT of the common carotid artery after adjustment for age (beta = - 3.57; 95% CI, - 6.34 to - 0.80). Higher serum total and free E2 levels were related to progression of IMT of the common carotid artery after adjustment for age (beta = 0.38; 95% CI, - 0.11 to 0.86; and beta = 0.018; 95% CI, - 0.002 to 0.038, respectively). These associations were independent of body mass index, waist-to-hip ratio, presence of hypertension and diabetes, smoking, and serum cholesterol levels Conclusions - Low free testosterone levels were related to IMT of the common carotid artery in elderly men independently of cardiovascular risk factors.