The case records of 36 cats and dogs undergoing surgical correction of a single extrahepatic portosystemic shunt were reviewed. In 12 animals, the shunt was fully ligated during the first surgical procedure, while, in the remaining 24, the shunting vessel could only be partially ligated. Assessment of serum bile acid concentrations demonstrated complete shunt occlusion in 15 of these latter 24 animals (63 per cent) between one and six months postoperatively. Ten animals (28 per cent) had persistently high serum bile acid concentrations postoperatively. Portovenogram findings in these individuals revealed six that demonstrated shunting solely through the original vessel; In five of these, full shunt attenuation was achieved at second surgery. Further shunt manipulation was not possible in the sixth case due to extensive adhesion formation. In the remaining four animals with raised bile acid concentrations, the portovenogram demonstrated shunting through the original vessel as well as the development of multiple acquired shunts.