We have studied by Spot Profile Analysis Low Energy Electron Diffraction (SPA-LEED) and Auger Electron Spectroscopy (AES) Ni-Al alloyed layers formed by annealing, around 780 K, Al deposits on a stepped Ni(111) surface. The surface structure and composition of the thin epitaxial Ni3Al and NiAl films, obtained respectively below and above a critical Al initial coverage thetac, differ markedly from those of corresponding bulk alloys. The Ni3Al ordered films form in a concentration range larger than the stability domain of the L12 Ni3Al phase. The NiAl films present a marked distortion with respect to the lattice unit cell of the B2 NiAl phase, which slowly decreases when the film thickness increases. It also appears that the value of thetac depends on the morphology of the Ni(111) substrate, increasing from thetac=4.5 ML for a flat surface to thetac =10 ML for a surface with a miscut of 0.4°. This could be directly related to the presence of steps, which favour Ni-Al interdiffusion.