The problems of high energy glancing-angle electron diffraction are discussed and the design of a diffractometer which largely overcomes them is described. This instrument is a reflection scanning electron diffraction system equipped with loss-electron filtering and two-dimensional scanning of the diffraction pattern. It is able to measure I(β, γ) as a three-dimensional display with an intensity accuracy to ±1%, provided the current exceeds 0.01 pA in the solid angle element, which is 10^-7 steradian in size. Filtering is to 6 ev in a 20 kev beam.The system has produced the first essentially elastic diffraction patterns from bulk grain-oriented and single-crystal materials. Removal of the loss electrons greatly improves contrast. Partial pressure of contamination must be reduced below 5 ntorr for true reflection diffractograms to be obtained.