It is the purpose of this paper to introduce and discuss the multi-beam-imaging (MBI) method for studying lattice imperfections in high-voltage electron microscopy. The image contrast is compared with the theoretical contrast based on the many-beam dynamical theory of electron diffraction; the effect of absorption is included in the calculation. It is shown that the nature of imperfections can be studied from only one image taken by the MBI method instead of the brightand dark-field images that are generally used. Further, the images of a thick crystal taken by the MBI method become much brighter than the ordinary bright-field and dark-field images. Finally, the technique is applied to the characterization of stacking faults and screw dislocations in thick regions observed in the 1 MeV electron microscope.