A new type of particle separator is proposed, namely a lung-like branched structure. The separation takes place as a consequence of the interplay between the flow characteristics in the branched geometry and the distinct inertial properties of the dragged particles. From the solution of the three-dimensional continuity and Navier-Stokes equations for the flow and transport equations for the particles, we can investigate how the resolution of the separation depends on the main geometrical parameters of the ramified structure, namely the angle and the homothety factor of the branchings, and the azimuthal angle between successive planes of bifurcation. Remarkably, our numerical results indicate that such a simple ramified geometry can be used as a flow device that is capable to separate particles with increased efficiency and over a broad range of Stokes numbers. (C) 2009 Elsevier Ltd. All rights reserved.