The　objective　of　this　study　is　to　investigate　the　hemodynamics　in　patient-specific　internal　carotid　aneurysm　and　discuss　the　reason　for　rupture　of　aneurysm.　A　3-Dimensional　pulsatile　blood　flow　in　internal　carotid　with　a　sidewall　aneurysm　was　studied　numerically　with　the　average　Reynolds　number　of　704.　Patient-specific　model　whose　parent　artery　has　a　large　＇S＇　bending　and　a　sidewall　aneurysm　was　constructed　from　CT　data.　Unsteady,　incompressible,　3-Dimensional　Navier-Stokes　equations　were　employed　to　solve　the　flow　field.　The　temporal　distributions　of　hemodynamic　variables　during　the　cardiac　cycle　such　as　streamlines,　wall　pressure　and　wall　shear　stress　(WSS)　in　the　arteries　and　aneurysm　were　analyzed.　From　streamlines　it　can　be　found　that　there　is　an　obvious　vortex　flow　in　aneurismal　cavity　in　a　cardiac　cycle.　The　type　of　this　vortex　flow　is　not　changed　in　a　cardiac　cycle.　As　far　as　Wall　Shear　Stress,　there　is　a　region　in　aneurismal　neck　where　the　value　of　WSS　is　relatively　high.　Growth　and　rupture　mechanism　of　internal　carotid　aneurysm　in　patient　can　be　analyzed　based　on　patient-specific　model　and　hemodynamics　simulation.　©　2011　IEEE.