Surface trapped hole centers have been generated by X-ray irradiation on an O-17 isotope enriched MgO sample. The resulting EPR spectrum allowed us to determine for the first time the complete O-17(-) hyperfine tensor (A = [18.6, 18.6, -104.8] G). Comparison of the measured data with those obtained by embedded cluster density functional theory calculations allows to identify the hole trapping center with three-coordinated oxide anions localized at MgO corners. (C) 2005 Elsevier B.V. All rights reserved.