The purpose of our research was to determine which groups and species of internal parasites endanger the health of sheep on the islands of Rab and Pag. The research was carried out in 10 flocks on both islands taking the fresh dung out of 30% of the total number of sheep in each flock. It was ascertained that the gastrointestinal parasites and protozoa of Eimeria genus are present in most flocks on both islands. The presence of the fluke Dicrocoelium dendriticum was ascertained in considerably larger number of flocks on the island of Rab than on the island of Pag. On the other hand, the presence of parasites of Moniezia and Nematodirus genus was ascertained in larger number of flocks on the island of Pag. In two flocks on Rab parasites of Protostrongylus genus were ascertained while on the island of Pag they were not found in any flock.