Computational　fluid　dynamics　analyses　were　performed　on　three　models　which　have　a　giant　aneurysm　with　or　without　a　stenosis.　The　first　is　a　model　with　an　aneurysm　(no　stenosis　and　no　stent),　the　second　is　a　model　with　a　preaneurysm　stenosis,　and　the　third　is　a　model　with　an　aneurysm　implanted　with　a　stent.　The　increase　in　pressure　in　aneurismal　sac　caused　by　a　50%　stenosis　is　about　10.3mmHg　at　peak　systole　(　comparison　between　the　second　model　and　the　first　model).　It　must　pay　attention　to　the　increase　of　the　pressure　for　the　patient　which　has　an　aneurysm　accompanied　by　a　stenosis　when　making　the　treatment　plan.　Otherwise,　it　may　cause　the　aneurysm　rupture.