The role of dispersion in the adsorption of cis- and trans-azobenzene on rutile TiO2(110) has been investigated by means of density functional theory methods. Dispersion is crucial to properly describe the relative values of the adsorption energy since it differently affects each isomer. Dispersion terms are also crucial to describe the energy reaction corresponding to the cleavage of the N=N azo bond. However, the main features of the interaction remain unchanged since the density of states, electron density difference plots and Bader charges are only slightly affected by the inclusion of dispersion terms. (C) 2012 Elsevier B.V. All rights reserved.