An efficient Lagrangian particle tracking module is developed for unstructured grids to analyze the deposition patterns in a CT based realistic extrathoracic airway model. Inhalation flow rates of 15, 30 and 60 l/min are considered with particle diameters ranging between 2 and 20 mu m. The complex flow patterns with skewed velocity profiles and flow separations are discussed. While most idealized mouth-throat models predict no transition for a flow rate of 15 l/min, we observe increase in kinetic energy levels soon after glottis, indicating the sensitivity to geometrical complexity at low flow rates. Mouth cavity acts as an effective filter and is responsible for a major percentage of total deposition for all three flow rates. Combining our model depositions with central bronchial tree depositions indicates that for normal breathing conditions, inspiratory deposition for the particle size 5 Pm, which is usually referred to as the upper limit of the respirable range for inhalation drugs, does not exceed 12%. (C) 2007 Elsevier Ltd. All rights reserved.