The karyotypes of Petrogale lateralis lateralis, P. I. purpureicollis and P. I. ‘Macdonnell Ranges’ were examined with G-banding from cultured fibroblasts. P. I. lateralis (2n = 22) was found to retain the plesiomorphic karyotype, whereas P. I. purpureicollis (2n = 22) and P. I. ‘Macdonnell Ranges’ (2n = 22) were found to share an apomorphic karyotype characterised by an acrocentric chromosome 3 (3a) and an acrocentric X-chromosome (Xp). Both the 3a and Xp can be derived from their respective P. I. lateralis homologues by centric transpositions. Although P. I. purpureicollis and P. I. ‘Macdonnell Ranges’ appear very similar chromosomally, they are readily distinguishable genically and morphologically, P. I. ‘Macdonnell Ranges’ being more similar to P. I. lateralis. Thus, in these taxa, genic and morphological divergence have not been associated with significant changes in karyotype.