Conflicting phylogenies have been proposed for the Chelidae (Testudines: Pleurodira), a family of side-necked turtles found only in Australasia and South America. Sequence data from the mitochondrial 12S rRNA gene were used to test these phylogenies. In total, 411 nucleotides were sequenced for each of 16 chelid species, including all 11 recognized chelid genera and, as outgroups, 5 genera of Pelomedusidae (Testudines: Pleurodira). Analyses using parsimony and neighbor joining algorithms strongly support the division of Australian Chelidae into the three monophyletic groups initially suggested by Burbidgeet al.(1974;Copeia2: 392–409):Chelodina(bootstrap value 99%), theEmyduragroup (87%), andPseudemydura.The analyses suggest that the Australian chelids are a monophyletic lineage (64%), with the Australian long-necked turtles,Chelodina,more closely related to the Australian short-necked chelids than to the long-necked South American species. These relationships are in contrast to those of Gaffney (1977;Am. Mus. Novitates2620: 1–28). The species of Australian long-necked chelids consistently form a monophyletic clade, withChelodina longicollisandChelodina oblongaas sister taxa. The data failed to resolve relationships among the Australian short-necked taxa:Emydura,theElseya latisternumgroup, theElseya dentatagroup,Rheodytes,andElusor.Unlike Gaffney (1977), we find some weak support (58%) forPseudemyduraas the closest relative of the other Australian short-necked taxa. With the exception ofHydromedusa,the South American taxa are monophyletic and the subgenera ofPhrynopsare paraphyletic.