The population biology of the long-nosed potoroo (Potorous tridactylus) was investigated at Barren Grounds Nature Reserve and Budderoo National Park in the Southern Highlands of New South Wales (NSW). Both study areas are important conservation reserves for this threatened species, with a large gap north (similar to 300 km) to the next known viable population on the mid-north coast of NSW at Mount Royal. Potoroos were live-trapped using bandicoot-sized cage traps, each set similar to 100m apart along walking tracks and fire trails. Trapping was conducted each autumn and spring over five years to enumerate the local population of potoroos and to describe their morphometrics. The local long-nosed potoroos were larger in size than those recorded to the south on mainland Australia, but smaller than those in north-eastern NSW, supporting the concept of a latitudinal cline in body size. Sexual dimorphism was observed, with adult males having larger body weights, head lengths and pes lengths. Between one-third and two-thirds of all males and females were captured in only a single trapping session, indicative of low levels of survivorship and/or high levels of dispersal or transience. Males regularly overlapped at trap sites with females, more so than with other males, while females rarely overlapped at trap sites. Barren Grounds Nature Reserve supported a larger number of potoroos and a greater degree of home range overlap between individuals.