The structure and vibrational spectra of HOBr calculated using ab initio post-Hartree-Fock methods are in reasonable agreement with experiment. Vertical excitation energies and oscillator strengths have been computed for transitions to low-lying excited states of HOBr. The peaks at 350 and 280 nm in the gas-phase absorption spectrum reported by Orlando and Burkholder (J. Phys. Chem. 1995, 99, 1143-1150) may be attributed to the (A) over tilde (1)A" and (B) over tilde (1)A’ states, respectively. The calculations predict another adsorption with a maximum at about 477 nm due to the (a) over tilde (3)A" state.