Museum specimens of seven Australian Pseudocheiridae (ringtail possums and greater glider) and six Australian Phalangeridae (brushtail possums and cuscuses) were examined to assess the extent of possible differences in gastrointestinal tract morphology and function within and between these two families of Australian folivorous possums. Although there were no differences between the two families in gut segment lengths, the Pseudocheiridae had less relative tissue mass in the small intestine (P < 0·05) and greater relative tissue mass in the caecum (P < 0·05) than the Phalangeridae. Total nitrogen concentrations of stomach, caecum and proximal colon digesta were greater in the Pseudocheiridae than in the Phalangeridae (P < 0·05), but in the distal colon they were similar. These differences suggest that the colonic separation mechanism previously documented in two pseudocheirid species is probably characteristic of the family Pseudocheiridae, but not of the Phalangeridae. They also reflect the more folivorous nature of the Pseudocheiridae, as leaves are generally higher than fruit in total nitrogen concentration. Among members of the Phalangeridae, there were no significant differences in any of the parameters measured, and it is concluded that the digestive strategy of the common brushtail possum (Trichosurus vulpecula) is probably representative of the family. In contrast, there were several notable differences among members of the Pseudocheiridae, indicating that the common ringtail possum (Pseudocheirus peregrinus) is not representative of all pseudocheirids. In particular, the digestive strategy of the rock ringtail possum (Petropseudes dahli) should be examined in relation to its unusual habitat, to its relatively simple caecum, and to the unusually low nitrogen concentrations found throughout its gastrointestinal tract.