Vascular diseases are the leading cause of death worldwide. Several causes contribute to the initiation and progression of these diseases, one of these causes is the hemodynamic effect of the flowing blood. The hemodynamic theory of atherosclerosis within blood vessels, especially (bends and bifurcations) needs further explanation and analysis. The present work was intended to simulate the blood flow within the carotid artery bifurcation (which is a very important site concerning the atherosclerosis and with direct relation to stroke) making use of Computational Fluid Dynamics (CFD). The work included the simulation of the induced Wall Shear Stress WSS between the blood and interior wall of the artery, also it included the simulation of blood flow using velocity pathlines and two dimensional velocity contours. The relation between WSS and atherosclerosis was studied. Also the flow of blood was studied and analyzed. The (CFD) simulation was performed using (ANSYS 14.0 Fluent).Three realistic geometrical carotid artery models were used for (CFD) analysis. Model 1 has represented normal, healthy artery, Model 2 also has represented normal, healthy artery but with larger bifurcation angle. Model 3 has represented a diseased carotid artery bifurcation with severe stenosis. The blood has been assumed to be Newtonian (which is a very accepted assumption regarding carotid artery) and the flow has been performed only during peak of systole and peak of diastole using flow waveform taken from literature. The results of CFD simulation have shown good agreement with previous experimental and numerical studies of various geometrical carotid artery models and have explained the effect of arterial geometry on blood flow. General WSS contours of model 1, 2 and 3 have shown good agreement with previous results in the relation of low WSS and atherosclerosis initiation, also the pathlines agreed very well with spiraling phenomena at sinus outer wall of internal carotid artery. It was concluded that the bifurcation angle affected the WSS magnitude and flow spiraling and secondary flow development at both internal carotid and external carotid arteries. The present study presents a promising technique for the accurate diagnosis of vascular diseases which help in improving the results of future vascular surgical operations and accurate decision making regarding atherosclerosis at carotid bifurcation and plaque rupture.