The morphology of single PWR UO2 fuel rods has been investigated by employing computerised gamma-ray transmission tomography. Four highly burnt fuel rods of different burnups (from 52 GWd/t to 126GWd/t) and a fresh rod have been investigated. This paper describes the tomographic station built to acquire the projections together with the related experimental procedure, followed by the description of the image reconstruction techniques implemented. The principal results obtained are presented and analysed at three levels. First, the derived linear attenuation coefficient matrix, which is very useful for the implementation of emission tomography, is discussed. Second, the variation of density as a function of rod radius is presented, showing an interesting morphological change of the fuel with burnup. Particularly for the highest burnup sample, the periphery is characterised by a lower density (a steep decrease of almost 10% from the adjacent region) characteristic of an ultrahigh-burnup high-porosity structure. Finally, the nondestructive derivation of the volume-averaged fuel density was performed, compared with other experimental data, and plotted as a function of burnup, so that an interesting linear relationship between density and burnup was established, providing a potential indicator for the noninvasive determination of nuclear fuel rod burnup. Atomic Energy Society of Japan.