LEED data from the stable 1*1 structure formed by exposing alpha -Fe(001) to oxygen at room temperature have been compared with full dynamical calculations. The oxygen atoms are found to lie at 0.53+or-0.06 AA above the surface in the four-fold hollows, and the spacing between the first and second iron layers is increased by about 7.5% to 1.54+or-0.06 AA.