The spin polarization of benzene molecules on an Fe(100) surface is investigated by density functional calculations and spin-polarized metastable-atom deexcitation spectroscopy (SPMDS). The spin asymmetry in the molecular orbitals, observed by SPMDS, does not decrease to zero at a multilayer coverage of benzene. Spin-resolved electronic states are calculated for several adsorption geometries. In double-layer adsorption, only the pi orbitals are spin-polarized, while sigma orbitals have no spin polarization. In tilted and edge-on adsorption, the spin polarization is negative at the molecular peaks and positive in the valley between two molecular peaks, which is in good agreement with the spin asymmetry at 8 L. (c) 2007 Elsevier B.V. All rights reserved.