The occurrence of Biomphalaria glabrata is recorded for the first time in the state of Piaui, where it was collected from several breeding places in the city of Parnaíba. Examination of 694 specimens showed that a part of them were infected with trematodes other than Schistosomatidae. So far no autochthonous cases of schistosomiasis have been identified in the city. The presence of B. glabrata in Parnaíba extends by 20 km eastward its range on the Northern Coastal Region of the Great Northeastern Region of Brazil, where it had been found as far as Araioses, on the eastern extreme of the state of Maranhão.