We have modelled the global magnetic field topology of the young, rapidly-rotating K0 dwarf AB Dor by assuming that the field is potential and using as a boundary condition Zeeman-Doppler images of the surface radial field obtained on three consecutive years. For each of the observed radial field distributions, we calculate the azimuthal component of the corresponding potential field. We then compare at each epoch (by means of cross-correlation) the potential and observed azimuthal field distributions and find that there is a good correlation for magnetic features at latitudes below 60$^\circ$. Above this latitude, the potential field fails to reproduce the almost unidirectional band of azimuthal field that is observed and the correlation is correspondingly poor.