High-level ab initio calculations, with and without solvent effects, were completed to resolve the contradictory experimental and theoretical results on the relative stabilities of the bisulfite ion, HOSO2-, and its tautomer, the sulfonate ion, HSO3-. Calculations at the G2 level reveal that the sulfonate anion is more stable in both the gas and aqueous phases by approximately 4-5 kcal/mol. Contradictory results were obtained if inadequate polarization functions were used on the sulfur atom. The gas-phase heat of formation, Delta H-f 298(o), for the bisulfite and sulfonate ions are respectively -165 and -169 kcal/mol. The first value compares favorably to the gas-phase experimental result equal to -165.6 +/- 2.5 kcal/mol for the bisulfite anion.