Up to six nematode species were identified from 86 specimens of the yellow-necked field mouse Apodemus flavicollis from three mountainous localities known as Avala, Cer and Liškovac in Serbia. The highest prevalence of infection of 97% was recorded from Mt. Avala. Only one nematode species, Syphacia frederici, occurred in all three localities. There was complete overlap in nematode species from Mts. Avala and Liškovac, whereas the taxonomic distinctness of Mt. Cer was seen in the presence of the insect-transmitted species Rictularia proni. Locality was a statistically significant factor in all the best-fitted generalized linear models of variation in abundances. The highest level of both species richness and parasite alpha diversity (Shannon's H= 1.47) was found in the easternmost Mt. Liškovac, whereas the diversity indices were lowest for the westernmost Mt. Cer (Shannon's H= 0.48). In view of this geographical difference, the beta diversity indices were calculated along a west to east longitudinal gradient.