Parasites of the round goby in the North-Western Black Sea region and the Gulf of Gdask have been investigated. Only Acanthocephalus lucii that infect the round goby from the Black Sea were found in one specimen from the Baltic Sea. A lot of the round gobys parasites are fresh water species (Diplostomum spp., A. lucii, Ergasilus sieboldi). The round gobys parasites which are most widespread in the Black Sea (Cryptocotyle spp., Dichelyne minutus) do not infect the goby in the Baltic Sea but are present for other fishes (Gobius niger, Platichthyes flesus). It is possible that the Baltic population of the round goby have a fresh water origin, because independently of the fact that marine parasites, Cryptocotyle concavum and D. minutus, inhabit the Gulf they do not infect the round goby.