Abstract During the preparation of thin samples of nickel oxide by ion-beam milling, it has been found that preferential removal of oxygen can occur to such an extent that islands of nickel metal form on the surface. The nickel islands are found to be aligned topotacticly with the oxide and the results are compared with other studies of the early stages of the reduction of nickel oxide. The shape of the islands is explained in terms of misfit dislocations which can accommodate the strain; the growth of the islands occurs by generation and climb of the misfit dislocations.