The geometries, vibrational spectra, and relative energetics of HBrO3 isomers have been examined using various ab initio and density functional [MP2, CISD, CCSD(T), and B3LYP] methods. The results show interesting trends for the HBrO3 isomers, The HOBrO2 isomer is found to be the lowest energy structure among the isomers, with an estimated heat of formation of 12.6 kcal mol(-1) at 0 K. We have examined the implication of the formation of tile HBrO3 isomers from the atmospheric cross-reactions of the HO2 and BrO species.