Structure and stability properties of the diatomic magnesium dication are studied by multireference configuration interaction methods within the Born-Oppenheimer approximation. Computing and investigating the potential energy curves of low-lying states, the electronic ground state (1)Sigma(g)(+) and several excited states of Mg-2(2+) are shown to support many vibrational levels that are almost stable against dissociative tunneling. (C) 2004 Elsevier B.V. All rights reserved.