The geometric structure of a NiO(111) film on Ni(100) has been determined by dynamical low-energy electron-diffraction analysis. The oxide film is sufficiently thick and uniform to carry out the analysis in the bulk crystal limit. Four orientational domains of NiO (111) are present. We consider four possible terminations of the oxide film (oxygen or nickel, fcc or hcp sites). Our results indicate that the oxide film terminates with a topmost layer of oxygen in fcc sites, and exhibits a 14.8% contraction in the first interlayer spacing relative to the "bulk" interlayer spacing of the film. The "bulk" lattice parameters of the oxide film are found to be uniformly compressed by 2.6% relative to bulk NiO(111). Comparison with other work suggests that oxygen termination, a strong contraction in the first interlayer spacing, and retention of cubic symmetry in deeper layers may be general characteristics of unreconstructed rocksalt(111) surfaces of metal oxide films.