Carpal anatomy in adults of 13 outgroup species and 50 diprotodontian species from all families except Tarsipedidae was examined, as well as a histological sectional series of a pouch young Vombatus ursinus. The results are discussed in the light of recent phylogenies, and functional aspects were considered to gain an understanding of carpal evolution in this diverse marsupial clade. Mapping of eight carpal characters on alternative diprotodontian phylogenies results in trees of similar lengths. Of the eight characters investigated, five characterize major diprotodontian clades and one offers an additional autapomorphy for the order. The occurrence of a prepollex varies across Diprotodontia, and for some species is polymorphic. Petauroids, Cercartetus and Trichosurus share the presence of a lunatum, a well-developed proximal process of the capitatum, a deep ulno-triquetral joint and a deep palmar process of the hamatum. Most macropodids are distinguished by the lack of a lunatum, lack of a proximal process of the capitatum, a short palmar process of the hamatum, a pointed ulno-triquetral articulation and a variably occurring groove in the scaphoid. The macropodines are set apart from the potoroines by their loss of a lunatum and a short palmar process of the hamatum. Two terrestrial clades, vombatiforms and macropodids, differ from the arboreal possums in similar aspects, indicating that carpal diversity might be related to function.