The main objective of this work is to investigate, by means of numerical simulation, the effects of the surface roughness on the laminar fluid flow through annular microchannels, and to propose a method to take into account the surface roughness effects in the calculation or simulation of the fluid flow through these microchannels. This method is based on the classical viscous flow equations, and consists in building an equivalent smooth channel with the same flow resistance as the "rough" one. (c) 2006 Elsevier Ltd. All rights reserved.