When subjected to plastic deformation, grains within ductile face-centred cubic polycrystals fragment into "soft", low dislocation density cells separated by "hard", dislocation-rich walls. Using a narrow-bandwidth, sub-micrometre X-ray beam, we have mapped the deformation structure inside a single grain within a deformed Ni polycrystal. Dislocation multiplication and entanglement was found to vary depending on the physical dimensions of the grain. The method we use overcomes current limitations in classical X-ray topography allowing topographic images to be formed from small, highly deformed grains. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.