Tree hollows are a key habitat component for a large number of Australian vertebrates and understanding how these resources are used is critical for developing successful management and conservation strategies for particular species or sets of species. Some hollow-using vertebrates are capable of using other kinds of nest sites. The common ringtail possum (Pseudocheirus peregrinus) is one of these species and it is known to use tree hollows and also to construct nests (dreys) made from sticks and leaves. Nest site selection by P. peregrinus may be a function of hollow availability. This proposition and several related questions were tested in a radio-tracking study that examined patterns of tree hollow and drey use by P. peregrinus in a range of vegetation types in Booderee National Park in Jervis Bay Territory. In addition, this study explored whether hollow and drey use was influenced by a wildfire that occurred in the study region in late 2003. It was found that use of hollows or dreys appeared to be a function of the availability of these resources. Most individuals were either primarily hollow users or primarily drey users. These patterns conformed to differences we recorded in hollow abundance between vegetation types: drey use was most pronounced in shrubland where hollows were rare and hollow use was most prevalent in forest where hollows were abundant. We found no evidence to suggest that hollow or drey use was influenced by fire. There was a trend pattern in our data suggesting that home-range size of P. peregrinus was larger in burnt versus unburnt sites but this effect was not statistically significant. Evidence was found that P. peregrinus selected particular kinds of trees as nest sites. Hollows in dead trees were more often used than those in living trees. Smaller dreys were most likely to be used. Several kinds of nest-selection effects that were contrary to the findings of studies of other arboreal marsupials were identified. These included more frequent use of smaller diameter trees with fewer cavities. The reasons for these unexpected results remain unclear. Findings such as those quantifying gender differences in the frequency of drey use, as well as marked between-vegetation-type differences in nest-type selection, indicate that nest use and nesting behaviour in P. peregrinus may be more complex than previously recognised. These findings also indicate that a deep understanding of the nesting biology of a species may require careful studies of both sexes, across a range of environments, and where disturbances have and have not occurred.