The study of parasitic fauna of the Gulf of Gdansk eel revealed the presence of the nematode Anguillicola crassus, not recorded in the area before. The relatively high level of infection (prevalence of 41.9%; mean intensity of 3.0 ind.) is indicative of the nematode posing a hazard for the Gulf of Gdansk eel population. More than half of the infected eel showed anatomo-pathological changes typical of anguillicolosis.