The thickness and temperature dependence of the angular distribution of the magnetic dichroism in photoemission from Co 2p core levels of Co/Cu(001) ultrathin films has been investigated, using unpolarized Mg Ka radiation. Photoelectron spectra were collected for emission angles in a range of ±9deg around the surface normal in the [001] azimuth. All asymmetry spectra were found to exhibit an identical spectral shape within the experimental error bar, but different scaling. The angular distribution of the Co 2p dichroic signal shows that at emission directions off the sample normal strong variations are present, in contrast to predictions from simple atomic theory. These crystallinity-related modulations were studied for Co films of different thicknesses (5, 3, 2, and 1.5 atomic monolayers (ML) and different temperatures (100 and 300 K). They are higher for thicker films and lower temperatures. This experimental finding proves a diffraction picture, in which this modulation around the surface normal is explained by diffraction effects in forward scattering along the sample normal. As diffraction effects in magnetic dichroism combine both diffraction and magnetic dichroism, its behavior is influenced by both, structural and magnetic properties of the film. (@@@)