The Giant Magnetoresistance (GMR) observed in magnetic multilayers is due to spin-dependent scattering of electrons at interfaces or bulk defects. In order to unambiguously separate these two possible contributions, we produced Fe/Cr superlattices with negligible bulk defects, thus providing only interface scattering. The vertical and lateral interface roughness parameters were quantitatively analysed using synchrotron X-ray diffraction and Conversion Electron Mossbauer Spectroscopy. The magnitude of the GMR effect depends on both the vertical roughness amplitude eta and the step density n(step). We find a linear increase of the Giant Magnetoresistance with eta x n(step).