We have completed a taxonomic revision of the New Zealand marbled skink (Cyclodina oliveri) species complex. Morphological analyses and mitochondrial sequence data (ND2, ND4, Cytochrome b; Total 1933 bp) are used to describe a new taxon (commonly known as the "Mokohinau" skink) and redefine C. oliveri. The morphological and molecular data indicate that C. oliveri is distributed on the Poor Knights Islands, Mercury Islands and Aldermen Islands. The new species is restricted to the Mokohinau Islands, Hen and Chickens group, Little Barrier Island and Great Barrier Island. Our data demonstrate that there is no support for the separation of the Poor Knights Islands population of C. oliveri from those on the Mercury Islands and Aldermen Islands. The genetic data indicate that C. whitakeri is part of the C. oliveri species group. Divergence time estimates indicate that the C. oliveri species complex diverged during the late-Miocene, with further divergences among island groups in C. oliveri including the origin of the new taxon during the late-Pliocene and mid-Pleistocene. We present a diagnostic key for Cyclodina.