During a long-term survey of the parasites of mammals from all over Bolivia, 44 individuals of Oxymycterus inca and 6 of Oxymycterus paramensis were collected and examined for parasites from the foothills and Eastern Cordillera (Los Yungas) of the Andes of Bolivia. Three species of nematode were found including, from the cecum, a previously unknown genus and species of pinworm, Caroloxyuris boliviensis n. gen, n. sp., aspidoderids representing Nematomystes rodentophilus, and from the stomach, Protospirura numidica criceticola. These helminths occurred in prevalences of 25, 9, and 14%, respectively, in O. paramensis. Caroloxyuris boliviensis resembles species included in the genus Syphacia in the structure of the cephalic mask and copulatory organs, and the extension of lateral alae. However, males of this species possess only 2 mamelons on the ventral surface of the body. Caroloxyuris can be recognized as being distinct from both Helminthoxys and Rauschtineria in the ornamentation of the mamelons and the shape of cephalic mask. A redescription of N. rodentophilus is provided, and Nematomystes scapteromi is transferred from Ansiruptodera to Nematomystes.