After experimental venous pouch saccular aneurysms were surgically fashioned on common carotid arteries of sheep, the ensuing long term hemodynamic effects on the vessel walls were examined up to seven years postoperatively. The aneurysms became more spherical rather than remaining elongated, enlarging at variable, individual rates. Venous sac changes were similar to phlebosclerosis in human veins with progression to sclerotic walls and loss of conventional mural architecture at most sites. Lipid accumulation, despite low serum cholesterol levels, calcification, intimal tears of variable depth, mural dissection and secondary mural thrombosis, occurred as in human atherosclerosis and indicated this model's potential for studies of such pathological disorders and the pathological effects of enhanced hemodynamic stress.