Only two of 49 cats undergoing surgical ligation of congenital extra- and intrahepatic portosystemic shunts died perioperatively, a mortality rate comparable with the mortality rates of dogs undergoing surgical attenuation of congenital portosystemic shunts and cats in which the shunts are attenuated with an ameroid ring constrictor. Thirty (83 per cent) of the 36 cats for which long-term information was available were still alive at a median follow-up period of 47 months (range six to 105 months); the outcome was excellent (no clinical signs) in 20 of them (median follow-up 37 months, range six to 105 months) and good (minimal clinical signs) in seven (median follow-up 39 months, range 10 to 73 months) and none of these 27 cats was on any long-term medication or special diet. The only major cause of morbidity was the development of neurological signs in 18 (37 per cent) of the cats. These included seizures and a wide variety of other neurological signs, and their development and persistence was not affected by the presence of preoperative seizures, the type of shunt, the degree of shunt attenuation or the age of the cat. The serum concentrations of ammonia and preprandial bile acids were normal or significantly below normal in the cats with neurological signs. Liver histopathology was similar in the cats with and without neurological signs. Ten (56 per cent) of the 18 cats that developed neurological signs recovered normal neurological function long term.