The nucleation of diamond on the zigzag and armchair edge atoms of the basal plane of hexagonal boron nitride (h-BN) has been investigated theoretically by using ab initio molecular orbital theory. The calculations have included the effects of electron correlation by means of second-order Moller-Plesset perturbation theory. Outgrowths corresponding to diamond nuclei are calculated to be energetically more stable than the corresponding growth of graphite nuclei, both on the zigzag edge and the armchair edge of the (001) plane of h-BN. A comparison between the nucleation of diamond on h-BN and on the corresponding graphite edges shows only small energy differences.