The three-dimensional crystal structure of isotactic polypropylene in its beta-polymorphic form has been refined against electron diffraction intensity data. Microtwinning by merohedry, probably in two antichiral domains in space groups P3(1) and P3(2), was identified by sharp continuous diffraction in h0l patterns from epitaxially crystallized samples. Nevertheless, a rather simple model of a frustrated chain packing could be improved by Fourier methods even though the solution of the structure by direct methods was itself frustrated by the extensive overlap of \F-hk0\ and \F-kh0\ or \F-hke\ and \Fhk.-e\ amplitudes which led initially to a false prediction of space group symmetry.