The photoionization efficiency (PIE) spectrum of OBrO was measured over the wavelength range lambda = 86-126 nm using a discharge flow-photoionization mass spectrometer (DF-PIMS) apparatus coupled to a VUV synchrotron radiation source. Bromine dioxide was generated in a flow tube reactor by first forming BrO via the reaction O(P-3) + Br-2 and then allowing the BrO to react on the cold flow tube wall. The PIE spectrum of the BrO reactant was obtained and the photoionization threshold evaluated from the half-rise point of the step at threshold. This remeasurement yields IE(BrO) = 10.48 +/- 0.02 eV, which supersedes our previous result. The PIE spectrum of OBrO displayed steplike behavior near threshold. A value of 10.29 +/- 0.03 eV was obtained for the adiabatic ionization energy (IE) of OBrO from analysis of the photoionization threshold at lambda = 120.5 nn. An ab initio determination of the IE of OBrO using the CCSD(T)/6-311+G(3dF)//CCD/6-311+G(3df) level of theory gives a value of 10.26 +/- 0.06 eV, which is in excellent agreement with the experimental result. The results are compared with previous determinations of the IE for both halogen monoxides, XO, and halogen dioxides, OXO (X = Cl, Br, I).