Many species of arboreal marsupials move regularly between den sites in hollow-bearing trees. We show, based on short-term radio-tracking data, that the Critically Endangered Leadbeater’s Possum Gymnobelideus leadbeateri can move 100 m (and sometimes up to 600 m) between den sites in hollow-bearing trees. These movement data have significant implications for the design of buffers of unlogged forest to protect colonies of Leadbeater’s Possum as well as for crude estimates of the species’ population size.