The lattice defects in polydiacetylene (PDA) single crystals prepared using physical vapor growth were investigated by white beam X-ray topography. Line patterns along the [001] and [102] directions were clearly observed. Appearance of the line patterns along the [001] direction proves the polymerization direction predicted by Hadicke et al. The topographic results are in good agreement with the surface morphologies investigated by atomic force microscopy (AFM). (c) 2005 Elsevier B.V. All rights reserved.