Although the results of limited side-to-side portacaval shunt were better than those of other shunts, postoperative encephalopathy still occurred in 10.2% of the patients. To determine the relationship between the diameter of anastomotic stoma and the development of postoperative encephalopathy, animal experiments and clinical observations were carried out. In 4 of 8 dogs in 3 months after limited side-to-side portacaval shunt and in 6 patients with postoperative encephalopathy, there was significant augmentation of the diameter of anastomotic stoma. To prevent the widening of anastomotic stoma caused by blood flow under high pressure, a limiting ring of 10 mm in diameter was put around the anastomotic site during operation in 21 patients with portal hypertension. Follow-up for 3-15 months (average 6 months) showed that there was no evidence of postoperative encephalopathy and rebleeding. A ring of same kind was put around the dilated anastomotic stoma during exploration in the 6 patients, and all their cerebral symptoms and signs disappeared completely soon after the second operation.