The Northern Gannet (Morus bassanus) is a large marine bird whose whole North American population breeds in waters of eastern Canada. Opportunities to identify causes of morbidity and mortality in recently hatched birds of this species are therefore limited to this region of North America. During the three decades since 1990 of wildlife health surveillance at the Atlantic regional center of the Canadian Wildlife Health Cooperative, what appears to be a previously undescribed syndrome of ischemic leg necrosis affecting mainly hatch-year Northern Gannets has emerged, which may relate to some unique aspects of the life history of these birds. This syndrome, observed in 14 birds, is characterized by severe necrosis and fibrinopurulent inflammation of soft tissues of the feet extending along the whole tarsometatarsus. An infectious cause is proposed to explain the pattern of lesions observed in these birds, possibly favored by a specialized and rich vascular system in their legs and feet. An acute or subacute cardiomyopathy, thought to be secondary to the severe leg lesions, was also observed microscopically in six of these birds.