The static defect structure of the oxygen ion conductor Y2O3 stabilized zirconia has been studied at room temperature by coherent diffuse neutron scattering from single crystal samples containing nominally 9.4, 12, 15 and 18 mol% Y2O3. There are two principal contributions to the observed diffuse intensity. The first arises from tetrahedral distortions in small vacancy free regions of the crystal which decrease in volume as the dopant level increases. The second arises from correlated vacancies and their associated relaxed ions in the remainder of the crystal. The 9.4 mol% sample has been studied at elevated temperatures. The scattering becomes partly quasielastic, but the correlations persist to the highest temperatures studied (1900°C). The temperature and Q-dependence of the energy width has been studied at selected positions in reciprocal space.