The structure of the triplet state of the hydrogen di-superoxide anion, [O-2-H-O-2](-), has been investigated by ab initio quantum chemical geometry optimizations. The anion has two short hydrogen bonds that are symmetry connected. At the highest level of theory considered (B3LYP/AUC-cc-pVTZ) the O-O bond length is 1.332 Angstrom, the hydrogen bond length is 1.220 Angstrom, the strength of the hydrogen bond is 155 kJ/mol and the standard enthalpy of formation of the anion is estimated to be -199 +/- 4 kJ/mol at 25 degrees C.