In a breeding group of Inca terns (Larosterna inca), 14 birds died without antemortem signs of illness. Other than a poor body condition and a bloody cloaca, no symptoms were observed. Gross necropsy revealed severe segmental hemorrhagic enteritis with intralesional trematodes in most birds. Histopathologic examination revealed infiltration of lymphocytes, plasma cells, and granulocytes in the lamina propria of the duodenum and cross-sections of trematodes in the lumen. The parasites were identified as Ichthyocotylurus erraticus, a trematode of fish-eating birds. The cause of the infestation most likely was the feeding of unfrozen fresh fish. We describe the first case of a lethal I. erraticus infestation in Inca terns.