Portosystemic shunts were ligated over a gauged stainless steel rod in 160 dogs and 15 cats, using a midline celiotomy. The diameter of the rod varied with the size of the shunt and the diameter of the portal vein cranial to the shunt. Shunts were narrowed to the smallest diameter that did not cause signs of portal hypertension such as cyanosis of the stomach, pancreas, and small intestine. A slight discoloration was accepted only if the heart rate, end‐expiratory CO2%, or arterial blood pressure (if available) did not deviate more than 15% from the values that were recorded at the beginning of the surgical procedure. The perioperative mortality (0–30 days) was 29%. The most common cause of death was euthanasia because of hypoplasia of the portal vein cranial to the shunt. Animals with intrahepatic shunts had a significantly lower probability of survival than animals with extrahepatic portocaval or portoazygos shunts. In dogs, large breed and a high body weight were also significant risk factors for non‐survival. Age had a significant effect on risk of non‐survival, with an increased risk for older dogs, irrespective of the breed of the dog (large breed vs. small breed). The probability of survival without recurrence of hepatoencephalopathy (HE) after 1 and 4 years was 61.3% and 55.7%, respectively. The only variable that was significantly associated with non‐recurrence of HE was the breed of the dog, there being a lower probability for large breeds. Among the animals that survived surgery for more than 30 days, there was a significant higher probability of recurrence of HE in cats than in dogs.