A morphologically distinct subspecies of black-footed rock-wallaby (Petrogale lateralis pearsoni) is naturally found only on North Pearson Island (~160ha) in the Investigator Group, SA, where it was isolated by rising sea levels ~10500 years ago. Subsequent translocations have seen additional populations established on Middle-South Pearson Island (~53ha) in 1960 and Wedge Island (96 ha) in 1975. We have used 10 hypervariable microsatellite loci to examine the levels of genetic diversity in the endemic (n=38) and translocated (n=45-77) P. l. pearsoni populations compared to mainland P. lateralis populations (n=19-52). Results show all sampled P. l. pearsoni populations have very low levels of genetic diversity (A=1.5-1.9; He=0.02-0.13) compared to mainland populations (A=3.5-12.7; He=0.54-0.87). Intriguingly more diversity was detected in the translocated Middle-South Pearson population than in its source population from North Pearson Island. In contrast the Wedge Island population was almost monomorphic. Overall, the severe loss of genetic diversity (up to 98%) in P. l. pearsoni populations appears to result from random genetic drift on a small isolated population, exacerbated by some subsequent one-off translocation events. Although additional supplementary translocations are recommended to enhance genetic diversity, populations of P. l. pearsoni are likely to remain inherently vulnerable to extinction and therefore of special conservation concern.