Angular neutron flux spectra leaking from iron slabs with various thicknesses up to 600 mm have been measured by the time-of-flight technique. The results are compared with calculations by the MCNP Monte Carlo code and the DOT3.5 two-dimensional discrete ordinates code with the JENDL-3 nuclear data file and with ENDF/B-IV. In the DOT3.5 calculations, a cross-section set with a selfshielding correction factor is also applied to examine its effect. The results show that the MCNP calculations based on both files agree very well for the main part of the deeply penetrating neutron spectrum, but the DOT3.5 code without a self-shielding correction underestimates the high-energy flux and the flux in the resonance energy range with increasing slab thickness. The self-shielding correction factor improves the underestimation, but the calculated flux is still smaller than the MCNP calculation.