We present a low energy electron diffraction study of the surface relaxation of MgO(100) at T = 80 K down to the second atomic layer using in situ cleaved MgO crystals. We find that the main perturbation from the bulk structure is a topmost surface layer rumpling of 3.3 +/- 1.5% and a very small second layer rumpling of 0.2 +/- 2%. In both cases the oxygen atom is displaced outward. The first interlayer spacing is slightly reduced by 0.2 +/- 0.7% whereas there is no change in the second interlayer spacing.