The results of NiMo/gamma -Al2O3 hydrodemetalation catalyst deactivation in a long-term test are presented. A residue from Maya crude has been processed in a continuous hydroprocessing unit provided with a trickle-bed reactor (TBR) at 648 K, 10 MPa H-2 pressure, 11/h g(cat) LHSV and 0.2 kg/kg ratio H-2/oil. Samples of catalyst from 100, 1100, 2100 and 3100 h on-stream have been characterised by Ni, V and Mo determination and the evolution of the structural and morphological characteristics of these samples has been followed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) using electron backscattering detector and microanalysis by dispersion of energies (EDS). XRD and XPS results have confirmed the presence of sulphide phases with a stoichiometry close to (V, Ni, Fe)(3)S-4. Metal deposition profiles of vanadium have shown high concentrations in the edges while nickel deposition profiles have been more uniform. The shape of these profiles has indicated that for vanadium removal reactions, the metal deposition process becomes more diffusion rate limited, resulting in a less deep penetration into the catalyst pellet.