We study the free expansion of a pancake-shaped Bose-condensed gas, which isinitially trapped under harmonic confinement and containing a vortex at itscentre. In the case of a radial expansion holding the axial confinement fixed weconsider various models for the interactions, depending on the thickness of thecondensate relative to the value of the scattering length. We are thus able toevaluate different scattering regimes ranging from quasi-three-dimensional (Q3D)to strictly two-dimensional (2D). We find that as the system goes from Q3D to2D the expansion rate of the condensate increases whereas that of thevortex core decreases. In the Q3D scattering regime we also examine afully free expansion in 3D and find oscillatory behaviour for the vortexcore radius: an initial fast expansion of the vortex core is followed by aslowing down. Such a nonuniform expansion rate of the vortex core impliesthat the timing of its observation should be chosen appropriately.