Background: Flow diverters (FDs) are increasingly used for bifurcation aneurysms. Failure of aneurysm occlusion may be caused by residual flow maintaining patency of the jailed branch along with the aneurysm. Methods: Sixteen wide-necked lingual-carotid artery bifurcation aneurysms were created in 8 canines. Patent aneurysms were randomly allocated 4 weeks later to flow diversion combined with jailed branch occlusion using coils and/or Onyx (n=6) or flow diversion alone (n=8). Angiographic results of aneurysm occlusion at three months were scored using an ordinal scale. Pathology specimens were photographed and neointimal coverage estimated. Results: Fourteen aneurysms were patent at one month. FD deployment was successful in all cases, but at 3 month follow-up, 3 devices had prolapsed into the aneurysm. None of the bifurcation aneurysms treated with FD alone were occluded at 3 months. Endovascular branch occlusion combined with flow diversion significantly improved aneurysm occlusion rates (median angiographic score of 2) compared to flow diversion alone (median score of 0: P=0.0137). Flow-limiting parent vessel stenosis was not observed in any arteries. Devices were covered with thick neointima in most cases. Conclusions: Treatment failures following flow diversion of bifurcation aneurysms can be caused by persistent flow to the jailed branch. Branch occlusion combined with flow diversion may improve angiographic occlusion of canine aneurysms.