The best surgical procedure to treat a carcinoma in the gastric cardia remains a controversy because the carcinoma is often advanced and there are other unknown factors. In this article the incidence of invisible metastasis from cardia cancer to the diaphragm will be analyzed using an experimental cardia cancer model and clinical studies. An experimental cardia cancer was induced by an endoscopic injection of VX2 cancer cells into the submucosal layer of the esophago-gastric junction in rabbits using a 27G needle and an Olympus BF-4B2 bronchofiberscope. A total of 26 cardia cancer models for Borrmann type 2 or 3 were produced. Of these, six (23%) had visible cancer metastases in the diaphragm, including 4 cases with direct invasion and 2 cases with peritoneal dissemination on the surface of the diaphragm. Four (20%) of the remaining 20 were histologically found to have macroscopically-invisible cancer metastases mainly in the lymph vessels of the left hemidiaphragm. From 1985 to 1988, 22 clinical cases of cardia cancer were managed by a combined total gastrectomy with a partial diaphragm resection through a left thoracoabdominal approach. When widely resected, reconstruction was performed using a latissimus dorsi muscle flap. Six (27%) of these 22 were also histologically found to have macroscopically-invisible cancer metastases to the diaphragm, including 1 (11%) of the 9 well-differentiated type and 5 (39%) of 13 poorly-differentiated type adenocarcinomas. For patients with stage II, III or IV cardia cancers with no hepatic metastasis and no peritoneal dissemination, the 2-year survival rate was 64% for those who underwent a combined resection of the diaphragm and 42% for those who underwent a non-combined resection. The postoperative mortality in this series was zero. This is the first report of invisible cancer metastases from cardia cancer to the diaphragm.