Results of limited side-to-side portacaval shunt is better than other shunts, but, post-operative encephalopathy was still observed in 10.2% of the patients. Therefore, animal experiments and clinical observations were carried out to determine the relationship between the changes in size of anastomotic stomas and the development of post-operative encephalopathy. It was shown that significant augmentation of the size of anastomotic stomas developed in 50% of experimental animals in a period of three months after limited side-to-side portacaval shunt and in all post-operative patients with post-operative encephalopathy. In an effort to prevent the enlargement of the anastomotic stoma caused by blood flow under high pressure, a limiting ring of 10 mm in internal diameter was put around the anastomotic site during operation in 9 patients with portal hypertension. These patients now have been followed up to 5-11 months without evidence of post-operative encephalopathy and rebleeding. A ring of the same kind was put around the enlarged anastomotic stoma during exploration in 6 patients with post-operative encephalopathy, and all the cerebral symptoms and signs disappeared completely soon after the procedure.