In recent years, simulations of the blood flow and the wall mechanics in the vascular system with patient-specific boundary conditions by using computational fluid dynamics (CFD) and computational solid mechanics (CSM) have gained significant interest. A common goal of such simulations is to help predict the development of vascular diseases over time. However, the validity of such simulations and therefore the validity of the predictions are often questioned by physicians. The aim of the research reported in this paper is to validate CFD simulations performed on patient-specific models of abdominal aorta aneurysms (AAAs) using patient-specific blood velocity inflow profiles. Patient-specific AAA geometries were derived from images originating from Computed Tomography (CT) or Magnetic Resonance (MR) imaging. Patient-specific flow profiles were measured with Phase-Contrast MR imaging (Quantitative flow, Qflow). Such profiles, determined at the inflow site of the AAA, were used as inflow boundary condition for CFD simulations. Qflow images that were taken on a number of planes along the AAA were used for the validation of the simulation results. To compare the measured with the simulated flow we have generated synthetic Qflow images from the simulated velocities on cut-planes positioned and oriented according to the planes of the validation images. The comparison of the real with the simulated flow profiles was performed visually and by quantitatively comparing flow values on cross sections of the AAA in the measured and the synthetic Qflow images. In a preliminary study on two patients we found a reasonable agreement between the measured and the simulated flow profiles.