The statistical analysis of human bronchial morphometry data reveals distinct asymmetric features of the airway branching pattern, which may greatly affect the localized distribution of particles deposited within airway bifurcations. Our analysis of particle deposition patterns within an asymmetric bifurcation is based on a recently developed numerical method for the calculation of air velocity fields and aerosol particle trajectories in a three-dimensional bifurcation model (Balashazy and Hofmann (1993) J. Aerosol Sci. 24, 745-772). In this numerical model, airflow is computed by solving the Navier-Stokes equations with a finite difference method, and trajectories of aerosol particles under the simultaneous action of inertial impaction, gravitational settling, Brownian motion, and interception are simulated by utilizing Monte Carlo techniques. In the present paper, the effects of asymmetry in airway diameter, branching angle, and flow division on both inspiratory and expiratory particle deposition patterns are explored for various particle sizes and flow rates. Model predictions are compared with the available experimental evidence, with other theoretical predictions, and with corresponding simulations for a symmetric bifurcation.