The diprotodontian family Petauridae is composed of two subfamilies: Petaurinae (gliders) and Dactylopsilinae (striped possums). Leadbeater's possum (Gymnobelideus leadbeateri) has generally been placed among the petaurines on the basis of morphological, particularly dental, characters. Recent microcomplement fixation data, however, suggest that G. leadbeateri is a sister group to the Dactylopsilinae. We report DNA-DNA hybridisation comparisons among Leadbeater's possum, two dactylopsilines, two petaurines, and an outgroup pseudocheirid. Phylogenetic analysis of these data support the basic dichotomy between petaurines and dactylopsilines, and suggest that G. leadbeateri is more closely related to dactylopsilines. Resolution of this relationship, assayed by bootstrap analysis, is limited, but branch lengths on the optimal tree suggest a rapid initial diversification of three lineages within the Petauridae: dactylopsilines, petaurines and G. leadbeateri.