Being able to recognise critical habitat features such as nesting and denning sites is essential for wildlife conservation. It is particularly true for the den trees of species threatened by habitat loss, such as the squirrel glider (Petaurus norfolcensis). Measurements of 146 den trees of the squirrel glider were made in fragmented woodlands of the South-west Slopes of New South Wales and data compared with random trees to quantify the key characteristics of den sites. The likelihood of use as a den tree increased with increasing numbers of visible tree hollows and tree size. Dieback was also a positive indicator of den use. However, when visible hollows within a tree are abundant, dieback-free trees were preferred. Measures of den tree context such as basal area, the number of neighbouring large trees and distance to the next nearest tree, were also found to be important determinants of the likelihood of usage. The above variables were combined into a multiple regression model. The squirrel glider favoured particular Eucalyptus species and some broader eucalypt groups. We believe such variations were most likely due to interspecific differences in hollow development and dieback among the various groups, rather than bark type, a factor previously cited as an important determinant of den tree usage. The ‘best’ model had high negative predictive power, suggesting it would be useful for identifying (1) trees that could be felled without a loss of this critical habitat resource (e.g. at development sites) and (2) areas unsuitable for potential squirrel glider relocation or habitat enhancement. Squirrel gliders show preference for a combination of tree and tree context features in selecting den trees. Understanding these features will help managers enhance and protect denning resources for this species.