The early stages of growth of polyaniline films electrodeposited on Au were studied by conventional electrochemical techniques, X-ray diffraction and ex situ scanning tunneling microscopy (STM). From high resolution STM imaging it appears that the first step of polyaniline formation involves the adsorption of aniline monomers on Au(lll) terraces leading to domains with hexagonal arrays involving a phenyl-phenyl distance in the range 0.70 nm less than or equal to d less than or equal to 1.0 nm. The second step corresponds to the initiation of the polymer growth yielding typically 10 x 10 nm(2) crystalline domains consisting of either 0.45 x 0.6 nm(2) rectangular arrays or 0.75 x 0.45 nm(2) arrays forming 120 degrees angles. The crystalline domains coexist with highly disordered polymer domains. At advanced stages of growth, the formation of polymer fibers 2 nm in average width takes place leading to a full substrate coverage by a polymer deposit with an irregular surface.