The objectives of this work were to reporte the helminths of the marine tucuxi, Sotalia fluviatilis (Cetacea: Delphinidae) in northern Rio de Janeiro State; and to check if the infestation rate varied with the host characteristics (sex and maturity) and year seasons. From 1989 to 2002, 80 marine tucuxis that were by-caught in fisheries were examined and four parasites were recorded: Braunina cordiformis, Anisakis typica, Halocercus brasiliensis and Nasitrema sp. The parasitism in the marine tucuxi corroborated its feeding habits and there were no infestation rate differences between males and females, youngs and adults, as well as between year seasons. This work reports for the first time the occurrence of the genus Nasitrema in the marine tucuxi.