The V-OH trapped-electron-hole center in magnesium oxide is studied with the periodic ab initio Hartree-Fock program CRYSTAL, by using the supercell scheme. The H atom that formally is substituted for a Mg atom at its lattice position migrates towards one of the neighboring O atoms, forming a strong covalent bond with it, whereas the hole localizes at the opposite O atom completely. The electronic structure of the defect is discussed in terms of electron charge and spin density maps and band structure. The isotropic and anisotropic components of the hyperfine coupling constant between the PI nucleus and the unpaired electron are calculated and are in quite good agreement with ENDOR results.