Nineteen wild ringed seals (Phoca hispida) were killed in winter 1999 to assess the health status of seals harvested in eastern Hudson Bay (Quebec, Canada). One of these seals, an 11-yr-old male, had a poorly differentiated adenocarcinoma that severely constricted the lumen of the distal small intestine. The tumor was characterized by proliferation of polygonal epithelial cells that formed closely packed acini and cords. This appears to be the first reported case of adenocarcinoma of the small intestine in Pinnipedia.