The vibrational structure of the photoelectron spectrum of the NO dimer is calculated by ab initio methods, and compared with the observed ZEKE (zero electron kinetic energy! spectra published by I. Fischer et al. [J. Chem. Phys. 96, 7171 (1992)] and A. Strobel et al. [J. Phys. Chem. 99, 872 (1995)]. The ground state potential of (NO)(2)(+) is calculated to have almost iso-energetic minima at planar cis (C-2v) and trans (C-2h) geometries, but the Franck-Condon factors from the ground state of (NO)(2) strongly favor transitions to the cis isomer. The good agreement for the vibrational frequencies and intensities shows that the (NO)(2)(+) isomer reached in the photoelectron spectrum has a cis-planar C-2v structure, rather than the twisted C-2 structure proposed by Fischer et al., or the trans-planar C-2h structure proposed by A. Strobel et al.