Gastric carcinoma has not been recognized as a complication of Gardner's syndrome in the Western world. We report a 37-yr-old white woman with Gardner's syndrome who had gastric adenocarcinoma in association with diffuse gastric polyps. At the time of laparotomy, the disease was metastatic to regional lymph nodes. In addition, the patient had mesenteric and retroperitoneal fibromatosis, thyroid adenomas, a chest wall hemangioma, and fibrocystic disease of the breast. This is the first reported case of gastric adenocarcinoma complicating Gardner's syndrome in North America.