In this study the biomechanical characteristics of a realistic carotid artery  are studied numerically using different inlet velocity profiles. Several experimental data measured  at the common carotid artery are used as inlet boundary conditions. Computation domain is generated using computed tomography (CT) data of a real patient. Three dimensional (3D) transient NS equations are solved, in this actual domain, using the proposed boundary conditions. Effects of different input conditions on the results of simulation are discussed. Main parameters such as velocity profiles, wall shear stress (WSS) and pressure distributions are investigated at the critical parts of the carotid artery such as bifurcation and sinusoidal enlargement regions. Results show that the input boundary conditions and slope/curvature discontinuities in the realistic geometry have strong relationship with the velocity, pressure and WSS distributions as expected. The most important conclusion obtained from our model is the existence of negative relation between velocity at several inner points of the internal carotid artery and velocity at the inlet of the common carotid artery. (C) 2013 Elsevier Ltd. All rights reserved.