A high‐temperature x‐ray‐diffractometer stage specifically designed for low‐angle work has been built. With careful alignment, the stage provides resolution sufficient to probe temperature‐induced structural changes in multilayers. A series of studies using the stage was performed on W/Cu multilayers with modulation wavelengths between 65 and 110 A˚ over the temperature range 25–180 °C. Reversible, temperature‐dependent changes in the modulation wavelength, and an irreversible increase in the intensity of the scattered radiation along both specular and nonspecular directions in reciprocal space, have been observed. The observed thermal‐expansion coefficients in the growth direction are marginally greater than would be expected from bulk behavior even when interactions with the Si substrate are taken into account. Analysis of the intensity changes indicates that, upon annealing, the interfaces within these multilayers become more rough, but that this roughness comes from a thermally induced buckling of the film. This results in a mosaic texture and increased reflectivity with a concomitant increase in diffuse scattering.