Photofragmentation of glyoxal, C2H2O2, under collision free conditions proceeds by internal conversion from S-1 to vibrationally excited S-0, which is observed to dissociate into H-2+CO+CO (28%), H2CO+CO (65%), and HCOH+CO (7%). Early molecular orbital calculations placed the barrier for the formaldehyde channel 12-20 kcal/mol above the three body fragmentation channel, contrary to what would have been expected from the branching ratios. The best calculational estimate of the barrier for the three body fragmentation was approximate to8 kcal/mol higher than the reported activation energy for the thermal decomposition of glyoxal. These problems have been resolved by the more accurate ab initio molecular orbital calculations reported in the present note. With the complete basis set extrapolation method of G. Petersson and co-workers using an atomic pair natural orbital basis set (CBS-APNO), the calculated heats of reaction that are within 0.4-0.8 kcal/mol of the experimental values for glyoxal-->H-2+2CO, H2CO+CO, and 2 HCO. The barrier computed for H2CO+CO is 54.4 kcal/mol, in excellent agreement with the high pressure limit of the activation energy for thermal decomposition of glyoxal. The computed barrier for the three body fragmentation is 4.8 kcal/mol higher than the H2CO+CO channel, in agreement with the observed lower yield for this channel.