One hundred rock ptarmigan (Lagopus muta), including 30 each of juvenile males and females, and 20 each of adult males and females, were collected in October 2006 in northeast Iceland to study their parasite fauna. Fourteen different parasite species were identified: 6 endoparasites (including the protozoans Eimeria muta, Eimeria rjupa; the heterokontophyt Blastocystis sp.; the nematodes Capillaria caudinflata and Trichostrongylus tenuis; and the cestode Passerilepis serpentulus) and 8 ectoparasites (including the feather mites Metamicrolichus islandicus, Strelkoviacarus holoaspis, Tetraolichus lagopi, and Myialges borealis; the feather lice Goniodes lagopi, Lagopoecus affinis, and Amyrsidea lagopi; and the louse fly Ornithomya chloropus). Blastocystis sp., P. serpentulus and A. lagopi are new host records. All parasite species showed aggregated distributions. Six species, E. rjupa, P. serpentulus, M. islandicus, G. lagopi, L. affinis, and O. chloropus, were more prevalent in juveniles than in adults, and 2 species, Blastocystis sp. and T. tenuis, were more prevalent in adults than in juveniles. The remaining species did not show age-related differences in prevalence. Blastocystis sp. is the only possible zoonotic parasite.