The electrooxidation of dihydroxymalonic acid (DHM) was investigated in neutral medium (0.1 M NaClO4) and dilute acidic medium (0.1 M HNO3) on polycrystalline platinum electrodes. Bulk electrolyses were performed mainly in diaphragmless cells, using suitable potential or current programmes (pulse electrolysis). The only carbon-bearing decomposition product formed proved to be CO2, with a current yield approaching 100% and zero-order kinetics with respect to the DHM concentration in solution.