NiAl2O4 is known to transform from a normal spinel, (Ni2+) [Al-2(3+)]O-4, to an inverse spinet, (Al3+)[Ni2+ Al3+]O-4, and vice versa. In this process, the larger Ni2+ ions which occupy the tetrahedral (8a) sites in normal spinel move to the octahedral (16d) sites in inverse spinel while half of the smaller Al3+ ions move in the opposite direction. The extent of this move is measured by the disorder or inversion parameter, I (the fraction of tetrahedral sites occupied by the At ions; I = 0 for normal spinet and I = 1 for inverse spinel). Previous studies suggest that the lattice constant of spinet can decrease as the disorder parameter increases to better accommodate the Ni ions. In situ neutron diffraction studies performed by us indicate that this process is also occurring during the reduction of NiAl2O4 to Ni and Al2O3. It is possible that the compressive residual stresses generated during reduction play a role in the structural evolution of NiAl2O4.