The electrochemical behaviour of monolayer and multilayer films of hexadecanoyltetrathiafulvalene, deposited on conductive substrates by the Langmuir-Blodgett technique, has been studied by cyclic voltammetry, chronoamperometry and visible/infrared spectroscopy. Monolayer films show stable reversible oxidation to the cation-radical state. However, in thicker structures, the electrochemical response is strongly distorted because of the hindered diffusion of ions.