The deposition of monodisperse aerosols entering an idealized oral cavity geometry through a variety of inlets was experimentally measured. Aerosol particles with diameters of 2.5, 3.8 and 5.0 mum were investigated at flow rates ranging from 15 to 90 L/min. The tested inlets ranged in diameter from 3 to 17 mm and included contraction nozzles, straight tubes, a turbulence generator and six commercially available dry powder inhalers (DPIs). A model for predicting the oral cavity deposition was derived from the data based on the particle Stokes number near the primary impaction location modified to incorporate the turbulent kinetic energy at the inlet. The model predicted similar (but slightly underestimated) deposition for monodisperse aerosols entering through DPIs, with increasing deposition for decreasing inlet diameter. The model was then extended to predict extrathoracic deposition for polydisperse aerosol formulations in vivo. Improved agreement was found between the in vitro predictions and the in vivo measurements compared to previous attempts. (C) 2003 Elsevier Ltd. All rights reserved.