This paper presents PIV measurements of the time-averaged flow field in the central sagittal plane of two realistic extra-thoracic airway (ETA) geometries with a constant inspirational flow rate of 90 l/min. Gamma scintigraphy measurements of regional deposition of 3 and 5 mum diameter particles in the same geometries under the same flow conditions are also presented. Comparison of the results reveals the strong connection between local deposition and the local fluid velocity field. Local deposition levels correlate very strongly with local levels of both velocity magnitude and flow curvature. This is consistent with inertial impaction being the dominant deposition mechanism. The two ETA geometries investigated are from the same subject and were obtained using magnetic resonance imaging (MRI). Three-dimensional computer-assisted drafting and rapid prototyping were used to build the casts. The results serve to illustrate the major effect intra-subject geometric variability can have on the ETA flow field and resulting regional deposition. (C) 2004 Elsevier Ltd. All rights reserved.