Electrochemical synthesis of polybithiophene films onto indium tin oxide was monitored by optical fixed-angle reflectometry in situ. Deposition was done in acetonitrile with NBu4PF6 as the supporting electrolyte at a scan rate of 100 mV.s(-1) using cyclic voltammetry. A correlation between the reflectometric output and the current density was observed. A mechanism to explain the shape of the reflectometric signal was proposed, based on ionic species motion (doping/undoping) and the state of oxidation of the film. The effects of several physico-chemical parameters were recorded. A low adsorbed amount of film was obtained when the monomer solution was injected when compared with electropolymerization in static conditions. Conversely, an increase in bithiophene concentration or a reduction in scan rate at 50 mV.s(-1) leads to thicker film. Finally a special reflectometric output was monitored when LiClO4 was employed as supporting electrolyte. (C) 2012 Elsevier B. V. All rights reserved.