Computational fluid dynamics (CFD) and magnetic resonance (MR) gas velocimetry were concurrently performed to study airflow in the same model of human proximal airways. Realistic in vivo-based human airway geometry was segmented from thoracic computed tomography. The 3D numerical description of the airways was used both for generation of a physical airway model using rapid prototyping, and mesh generation for CFD simulations. Steady laminar inspiratory experiments (Reynolds number Re = 770) were performed and velocity maps down to the 4_th airway generation were extracted from a new velocity mapping technique based on MR velocimetry using hyperpolarized ³He gas. Full 2D maps of the velocity vector were measured within a few seconds. Numerical simulations were carried out with the experimental flow conditions and the two sets of data were compared between the two modalities. Flow distributions agreed within 3%. Main and secondary-flow velocity intensities were similar, as for velocity convective patterns. This work demonstrates that experimental and numerical gas velocity data can be obtained and compared in the same complex airway geometry. Experiments validated the simulation platform that integrates patient-specific airway reconstruction process from in vivo thoracic scans and velocity field calculation with CFD, hence allowing the results of this numerical tool to be used with confidence in potential clinical applications for lung characterization. Finally, this combined numerical and experimental approach of flow assessment in realistic in-vivo based human airway geometries confirmed the strong dependence of airway flow patterns on local and global geometrical factors, which could contribute to gas mixing.