Most parts manufactured by Liquid Composite Molding (LCM) are thin shells, i.e., the resin flow in the mold can be approximated by a two-dimensional mathematical model based on Darcy’s law. However, for thick composite parts three-dimensional mold filling simulations are necessary. This results in much longer calculation times. The goal of this paper is to study the accuracy of mold filling simulations carried out by finite elements and to compare the accuracy of 2D versus 3D calculations. The simulation software used in this analysis, LCMFLOT, was developed by the Centre of Applied Research on Polymers of Ecole Polytechnique, Montréal. The accuracy of the algorithm is studied for conforming and non conforming finite elements using different meshes. Examples of simulation are first carried out for a simple ribbed test part. The results of 2D and 3D simulations are discussed for different geometrical parameters and pressure or flow rate injection boundary conditions. Finally, results of validation for three-dimensional complex industrial parts are presented.