Gadolinium/molybdenum multilayers have been prepared by dc magnetron sputtering and their structure has been investigated by transmission electron microscopy and low-angle x-ray diffraction. The in-plane magnetization of a series of multilayers with the same molybdenum layer thickness but different gadolinium layer thicknesses has been measured in fields up to 7 T at temperatures between 5.5 K and 250 K. The magnetic behaviour of the multilayers has been interpreted on the basis of a simple model of their magnetic structure. The interfaces between the gadolinium and molybdenum layers have significant roughness which increases as the layer thicknesses increase, and this roughness affects the magnetic behaviour of the interface regions, preventing the gadolinium moments near the interfaces from aligning with the applied field.