The specularly reflected intensity from cadmium arachidate multilayers has been measured as a function of incidence angle. The films were prepared by the Langmuir-Blodgett technique and ranged from three to 21 layers in thickness. Monochromatic synchrotron radiation of 1560 eV photon energy (wavelength 7.95 Å) was used in combination with a high vacuum compatible triple-axis diffractometer. The measured diffraction profiles were fitted with a theory based on the exact solution of the Fresnel-Bragg equations for multiple reflections including absorption. The optical parameters for the layers were taken from tabulated values, and the layers were constructed using a formulation similar to that employed previously by Pomerantz and Segmüller. The individual layer spacing as well as the total thickness of the film could be derived to within an accuracy of 1% or 1 Å (whichever is larger). © 1989.