The objective of the present study was to determine the viscoelastic properties of the common carotid artery in 35 patients with aortic aneurysm before surgery (AAA) (age 71 years, range 61-84), in comparison with 48 patients with essential hypertension (HT: 50 years, range 24-88) and 44 normotensive subjects (NT: 44 years, range 23-85). The second objective was to establish the relations between common carotid artery (CCA) viscoelastic properties and histologic lesions observed on AAA segments, obtained after surgery. CCA diameter was larger and distensibility smaller in AAA patients than in HT and NT. Distensibility of the aortic aneurysm was smaller than that of upstream 'normal' aorta, itself being smaller than control aortas. AAA wall lesions were extensive, associating adventitial and medial fibrosis, elastolysis, smooth muscle rarefaction, neovascularization, inflammation and plaques. The grade of these lesions was not correlated with the mechanical properties of the aorta and CCA; however, they could explain their qualitative alterations. AAA is characterized by severe stiffening and dilatation of large arteries distant from the aneurysm location. Whether this pattern of arterial phenotype is explained by the increase in stiff material (collagen) and the rarefaction of distensible material (smooth muscle and elastin) remains to be determined.