Electrochemical oxidation of arylhydrazides Ar-CO-NH-NH-R does not lead to the expected benzaldehydes. For R = H, benzoic acids and eventually diaroylhydrazines are obtained; in the special case of o-nitrobenzoylhydrazine, unexpected formation of o-nitrosobenzoic acid is observed. For R = Ph, oxidation is a two-electron process leading to unstable 1-aroyl-2-phenyl-diimides; the latter can be trapped with p-toluenesulfinic acid when electrolysis is carried out in a water-acetonitrile mixture.