This study evaluates the efficacy of dual Willis covered stents for the treatment of large fusiform carotid aneurysms in a canine model. Carotid fusiform aneurysms >10 mm long were surgically created in 10 dogs and were then repaired using either single or dual covered stents. Clinical results were assessed by scheduled angiography and histological features by light and electron microscopy. Angiography immediately post-op and 6 months after surgery revealed aneurysm isolation rates of 60 and 20% for the single stent technique and 60 and 100% for the dual stent technique, respectively. The rate of complete obliteration of the aneurysm sac differed significantly between treatments (P = 0.048). The dual stent technique also resulted in greater endothelialization. For large carotid fusiform aneurysms in a canine model, endovascular repair using dual Willis covered stents is technically feasible and more effectively obliterates the aneurysm sac than the use of a single stent.