High-level ab-initio studies were performed to investigate the stability of halosulfite ions. The basis set 6-31+G(3df) was used for the fluorosulfite and chlorosulfite ions. Pseudopotential functions were used for describing the core electrons of the heavier halogen atoms. Hartree-Fock and MP2 optimizations were carried out, and various levels of theory up to QCISD(T) were used for the energy calcns. Addnl. calcns. were performed to investigate the stability of the ions in polar environments. The calcd. stability trend with respect to halosulfite ion formation from SO2 and the halide ion (SO2F- (~50 kcal mol-1) .mchgt. SO2Cl- (~20 kcal mol-1) > SO2Br- (~18 kcal mol-1) > SO2I- (~13 kcal mol-1)) is in agreement with the exptl. obsd. trend. From these calcns., only the fluorosulfite ion appears to be stable in polar solvents, while all the other anions may dissoc.