Currently available animal models for the study of treatment of aneurysms are either expensive or yield unreliable results. An animal series was devised to address both of these problems by creating a new animal model. Twelve Sprague-Dawley rats were used to demonstrate that a vein-pouch aneurysm could be constructed at a surgically created carotid bifurcation. Patency rates, growth dynamics, and histologic morphology were studied at three time intervals. A 100% patency rate at the aneurysm orifice was achieved with one-third of the aneurysms showing varying degrees of partial apical thrombosis. A growth pattern was established over the study period. Magnetic resonance angiography and digital subtraction angiography were successfully employed to study a small number of additional aneurysms. Our conclusion is that a bifurcation aneurysm can be constructed in the rat with high patency rates and predictable saccular morphology which resembles most human intracranial aneurysms. This inexpensive animal model can be used to study novel modalities for the treatment of aneurysms.