Multiplexed holographic structures have been suggested to provide large capacity and parallel access as three-dimensional storage media. One of the most widely used techniques in the literature for analyzing such structures has been the coupled-wave analysis and its variations. Another approach that is becoming increasingly popular because of the ease with which it can be implemented is the beam propagation method (BPM). The BPM is quantitatively compared with the rigorous coupled-wave analysis for the cases of single and multiplexed gratings. Normal and off-normal incidence as well as TE and TM polarizations are considered for single (slanted and unslanted) and multiplexed gratings. It is shown that the BPM, even in its most rudimentary form, is a powerful and accurate calculational method that is especially suited for analyzing the many multiplexed grating diffraction problem.