Reorientation in the magnetic anisotropy as a function of film thickness has been observed in Co-Ni and Co thin films, obliquely sputtered on a polyethylene terephthalate substrate at a large incidence angle ͑70°͒. This effect is a consequence of the low magnetocrystalline anisotropy of the films ͑fcc structure of Co͒ and changes in microstructure from nuclei to columns according to the thickness. The critical thickness for this transition was estimated to be 30 nm for Co-Ni.