The electronic structure of the rutile(110) surface after formation of an isolated oxygen vacancy has been studied with density functional (DF) calculations and TiO2 embedded clusters. Restricted and unrestricted open shell wave functions have been analyzed in terms of atomic spin densities and Ti core level shifts. The removal of a neutral oxygen atom from the bridging oxygens of the TiO2(110) surface results in two unpaired electrons localized at the 3d orbitals of neighboring 5-coordinated Ti atoms. The electronic structure of an O vacancy on the surface of TiO2 is compared with that of the same defect in MgO and SiO2. (C) 2002 Elsevier Science B.V. All rights reserved.