Photodissociation of glyoxal via the H2CO+CO channel has been investigated by ab initio classical trajectory calculations using Becke's three-parameter hybrid functional method with split valence and polarized basis set [B3LYP/6-311G(d,p)]. To model the experimental conditions, trajectories were started from a microcanonical ensemble at the transition state with 8.5 kcal/mol excess energy distributed among the vibrational modes and the transition vector. The CO product was produced with a broad rotational distribution but with almost no vibration excitation. When combined with the results from the H-2+2CO channel, the calculated vibrational and rotational distributions of CO are in excellent agreement with the experimental observations. The rotational distribution of H2CO was very broad ranging up to J=85. The H2CO product has significant vibrational excitation in the out-of-plane bending, CH2 rocking, CH2 scissoring, and CO stretching modes. For both the H-2+2CO and the CO+H2CO channels, the majority of available energy was partitioned into translations.