In present study, an anatomically accurate, validated in the entirenonlinear domain, three-dimensional finite elementmodel was used to investigate the biomechanical effects of facetectomy on the stability of the human lumbosacral spine. Bilateral total facetectomy was simulated at L4-L5 and L5-S1 levels. Flexion, extension, and axial torsion were applied using pure moment protocols. Total facetectomy increased spinal instability significantly under extension and axial rotation and not under flexion.