A new species, Montistrongylus karungi (Heligmonellidae) was collected from the digestive tracts of 6 Abeomelomys sevia (Rodentia: Muridae: Anisomyini) from localities in the Highlands of Papua New Guinea. The new species differs from both its congeners in having 13–18 ridges in the synlophe. Larval Ophidascaris (Ascarididae), Heterakis sp. (Heterakidae), and Odilia mackerrasae (Heligmonellidae) were each recovered from a single host. The phylogenetic relationships of Abeomelomys within the Anisomyini are as yet unresolved, and there is insufficient information about the helminth assemblages of the ansomyin genera, but there are similarities in ecology and distribution of the hosts of the 3 species of Montistrongylus. Therefore it is unclear as to whether coevolution, host switching, or both have been influential in speciation.