After edge-rolling (heavy width-reduction), the cross-section of a continuously-cast steel slab may be non-rectangular, whereas what is desired is that it should be exactly rectangular. The deformed shape results in an increased number of heavy width- and thickness-reductions having to be imposed on the slab. Since edge-rolling is clearly a three-dimensional forming process, use of plane-strain analysis would be insufficient: a three-dimensional finite-element formulation, based on elastic-plastic material behaviour, has therefore been developed. This three-dimensional formulation has been incorporated into the existing special purpose FEM programme DIEKA, developed at Twente University of Technology by one of the present authors. The former two-dimensional programme DIEKA has already been successfully applied to plane-strain processes such as the cold rolling of strip-material, and axi-symmetric processes such as wire drawing. Using the extended three-dimensional programme, calculations have been made in order to investigate the influence of roller-radii on the resulting cross section of the slab after a width reduction. Experiments for verification and small-scale simulation of the real production process have been carried out using plasticine as a model material.