Pachyarmatherium is an enigmatic cingulate genus formerly recognized as Dasypodoidea, but tentatively assigned to the poorly known subfamily Glyptatelinae (Glyptodontidae) by later authors. A new species is described from the late Pleistocene of northeastern Brazil. The material comprises several isolated osteoderms, carapace fragments, and miscellaneous postcranial material. The new species, Pachyarmatherium brasiliense, differs from the North American Pachyarmatherium leiseyi in being larger and in having osteoderms with heptagonal shape, main figures with oblong, subrounded and polygonal outline (instead of only polygonal), and a larger number of peripheral figures. To clarify the affinities of Pachyarmatherium, a cladistic analysis was conducted of 48 morphological postcranial characters and scored for 11 cingulates (the new species, four dasypodids, one pampathere and five glyptodontids) and two pilosans used as outgroup taxa. In the most parsimonious topology obtained, Pachyarmatherium is the sister-group to a clade including Pampatheriidae and Glyptodontidae. This result contradicts the previous tentative allocation of Pachyarmatherium to the Glyptodontidae, and indicates that the glyptodont-like characters of the carapace and osteoderms of Pachyarmatherium are homoplasies shared with glyptodonts. The taxonomic validity of the genera Pachyarmatherium and Neoglyptatelus is recognized, but the morphological evidence from the external ornamentation of osteoderms does not offer support for the placement of Pachyarmatherium within Glyptatelinae.