[en] A triple axis X-ray spectrometer has been used to test the smoothness of mirrored surfaces. A perfect channel-cut Si or Ge crystal extracts Fe-kα /sub radiation from a conventional X-ray tube. The radiation is incident on the test surface and the specularly reflected and scattered radiation from the surface is analyzed by another perfect channel-cut Si or Ge crystal. The channel-cut crystals provide an essentially ''tailless'' probe of the scattered radiation. The test surfaces in this study include three standard flats from the EXOSAT program, the AXAF-program and the ROSAT program, respectively, and test foils made in connection with the construction of a high throughput thin foil reflector telescope for the ESA X-ray Spectroscopy Mission XMM