The structure and properties of stoichiometric iron oxide clusters (FeO)n are computed using all-electron density functional theory (DFT) for n > 10. The structures of (FeO)11, (FeO)13, (FeO)14, (FeO)15, and (FeO)16 clusters are reported for the first time. Their lowest total energy states are found to possess spin multiplicities of 5, 5, 47, 27, and 15, respectively. The geometrical structure of the lowest total energy state of a (FeO)n cluster corresponds to chemisorption of oxygen atoms on the surface of the corresponding unary Fen cluster when n > 12. Computed properties of the iron oxide clusters are compared to the properties of the corresponding bare iron clusters. The average binding energy per atom of a (FeO)n cluster is substantially larger than that of Fen at all n. Surprisingly, the values of both polarizability and binding energy per atom of the iron oxide clusters change insignificantly when n increases from two to 16. In order to compare the performance of DFT methods in the iron and iron oxide series, the states of Fe8 and (FeO)8 were computed using five exchange–correlation functionals in the whole range of possible spin multiplicities. It is found that the results of computations of the (FeO)8 cluster are more sensitive to the choice of a DFT functional than those of the Fe8 cluster.