To assess outcomes of dogs with side-to-side portocaval extrahepatic portosystemic shunts (PC-EHPSS) and poor portal perfusion to the liver treated with medical management alone (MM) or surgical attenuation (SA). Multi-institutional retrospective study. A total of 21 dogs with PC-EHPSS (14/21 MM and 7/21 SA). Medical records were reviewed, and data was collected on dogs <12 kg with PC-EHPSS treated with MM or SA between June 2008 to June 2021. Signalment, clinical signs, postoperative complications, bloodwork values, long-term clinical outcome, survival, and owner reported quality of life were recorded. Of 21 dogs included, 10 were mixed breeds and 14 were females. Median age at time of presenting clinical signs was 163 days. At final follow-up examination (median 1119 days), all SA and 6/14 MM dogs were alive, with a median survival time of 2138 days following treatment onset. In surviving MM dogs, outcome was fair in 3/6 and poor in 3/6. In SA dogs with long-term follow-up, outcome was fair in 5/6, and poor in 1/6. A greater proportion of SA dogs had improved bloodwork parameter values at final follow-up examination, and the mean relative change in final bloodwork values was higher when compared to MM dogs. These findings demonstrate that SA has improved clinical outcomes to MM for PC-EHPSS; however, SA clinical outcomes appear worse than those previously reported for other EHPSS. This information may have implications for expected outcomes in other EHPSS subtypes associated with severely diminished portal perfusion.