The morphology of the periotic in the extant trichosurin possums Strigocuscus celebensis and Wyulda squamicaudata is described and compared with that of various species of extant and extinct phalangerid marsupials. The periotic morphologies of S. celebensis and W. squamicaudata show a number of similarities with those of brushtailed possums of the genus Trichosurus, strengthening the case for a monophyletic tribe Trichosurini consisting of these three genera. Comparisons with periotics of possums from the Tertiary Riversleigh deposits of Queensland that were previously assigned on the basis of craniodental anatomy to Trichosurus and Strigocuscus suggest that, despite some similarities, the three extant trichosurins may be more closely related to each other than to the Riversleigh taxa. A revised morphological diagnosis of the Trichosurini is provided, incorporating these data.