Striped possums (Dactylopsila trivirgata) are small arboreal marsupials for which limited medical information is known. Mastophorus muris is a gastric spirurid nematode of rodents that uses insects as intermediate hosts. Three cases of gastric spiruridiasis caused by M. muris in captive striped possums are reported for the first time. Diagnosis was made by the presence of adult nematodes in regurgitant and at necropsy. Low numbers of nematode ova shed intermittently in possum feces made evaluation of treatment success difficult. No histopathologic abnormalities were identified in one case. Control of M. muris in captive possum colonies may be achieved by interrupting the life cycle of the parasite.