We report a photoelectron imaging study of the radical-anion of glyoxal. The 532 nm photoelectron spectrum provides the first direct spectroscopic determination of the adiabatic electron affinity of glyoxal, EA = 1.10 +/- 0.02 eV. This assignment is supported by a Franck-Condon simulation of the experimental spectrum that successfully reproduces the observed spectral features. The vertical detachment energy of the radical-anion is determined as VDE = 1.30 +/- 0.04 eV. The reported EA and VDE values are attributed to the most stable (C-2h symmetry) isomers of the neutral and the anion. (C) 2016 Elsevier B.V. All rights reserved.