Arteriographic measurements were made in 73 consecutive women undergoing arterial reconstruction for aorto-iliac occlusive disease. The anatomical distribution of atherosclerosis was unaffected by arterial size. Women with isolated aorto-iliac atherosclerosis had the same size arteries as those with concomitant outflow disease. Aortic, iliac, and femoral artery diameters were distributed as a single group, with no distinct subgroup of "small arteries." However, women whose aorta was less than 1 S.D. below the mean were younger and had less cardiovascular disease even when the effects of age and body size on arterial diameter were excluded. Women with this statistical definition of "small aorta" were clinically analogous to those previously identified anecdotally. The authors propose that a "small aorta" in a women with aorto-iliac atherosclerosis be defined as less than 19 mm in diameter above and less than 13 mm below the renal arteries and less than 10 mm at the bifurcation.