  The resistance of multilayers with interface roughness on a length scale
which is large compared to the atomic spacing is computed in several cases via
the Boltzmann equation. This type of roughness is common in magnetic
multilayers. When the electronic mean free paths are small compared to the
layer thicknesses, the current flow is non-uniform, and the resistance
decreases in the Current-Perpendicular-to-Plane (CPP) configuration and
increases in the Current-In-Plane (CIP) configuration. For mean free paths much
longer than the layer thicknesses, the current flow is uniform, and the
resistance increases in both the CPP and CIP configurations due to enhanced
surface scattering. In both the CPP and CIP geometries, the giant
magnetoresistance can be either enhanced or reduced by the presence of long
length scale interface roughness depending on the parameters. Finally, the
changes in the CPP and CIP resistivities due to increasing interface roughness
are estimated using experimentally determined parameters.
