Preliminary research suggests that Australia's endemic rainforest possums will have reduced distributions, and likely face extinction as a result of climate change effects [1-2]. However these predictions have lacked information about their physiological thermal tolerances and the thermal selections of denning or roosting sites in which these nocturnal marsupials shelter during the heat of the day. We present here information about the thermal qualities of the dens and roosts selected by green ringtail possums (Pseudochirops archeri), Herbert river ringtails (Pseudochirulus herbertensis), and lemuroid ringtail possums (Hemibelideus lemuroides) relative to that of the surrounding environment, and describe the thermal tolerances of these species. This new knowledge provides more accurate predictions of the effects that extreme temperatures may have on these species, and gives insight into how other tropical arboreal mammals may be able to behaviorally moderate the temperatures to which they are exposed.