The kinetics of the reaction HBrO2 + HBrO2 -> HOBr + BrO3- + H+ is investigated in aqueous HClO4 (0.04-0.9 M) and H2SO4 (0.3-0.9 M) media and at temperatures in the range 15- 38 degrees C. The reaction is found to be cleanly second order in [HBrO2], with the experimental rate constant having the form k(exp) = k + k'[H+]. The half- life of the reaction is on the order of a few tenths of a second in the range 0.01 M < [ HBrO2](0) < 0.02 M. The detailed mechanism of this reaction is discussed. The activation parameters for k are found to be E-double dagger = 19.0 +/- 0.9 kJ/ mol and Delta S-double dagger = -132 +/- 3 J/(K mol) in HClO4, and E-double dagger 23.0 +/- 0.5 kJ/ mol and Delta S-double dagger = -119 +/- 1 J/( K mol) in H2SO4. The activation parameters for k' are found to be E-double dagger = 25.8 +/- 0.5 kJ/ mol and Delta S-double dagger = -106 +/- 1 J/( K mol) in HClO4, and E-double dagger 18 +/- 3 kJ/ mol and Delta S-double dagger = -130 (11 J/( K mol) in H2SO4. The values Delta H-f(298)0 {BrO2( aq)}) = 157 kJ/mol and Delta H-f(298)0 {HBrO2(aq)}) -33 kJ/mol are estimated using a trend analysis (bond strengths) based on the assumption Delta H-f(298)0 {HBrO2( aq)} lies between Delta H-f(298)0 {HOBr(aq)} and Delta H-f(298)0 {HBrO3(aq)} as Delta H-f(298)0 {HClO2(aq)} lies between Delta H-f(298)0 {HOCl(aq)} and Delta H-f(298)0 {HClO3(aq)}. The estimated value of Delta H-f(298)0 {BrO2(aq)} agrees well with calculated gas-phase values, but the estimated value of Delta H-f(298)0 {HBrO2(aq)}, as well as the tabulated value of Delta H-f(298)0 {HClO2(aq)}, is in substantial disagreement with calculated gas-phase values. Values of Delta H-r(0) are estimated for various reactions involving BrO2 or HBrO2.