Case records of 27 dogs with medically managed congenital portosystemic shunts were reviewed. Fourteen were followed up by telephone questionnaires to the owners. Age, breed, sex, clinical signs and blood results were similar to previous studies. Weight and quality of life were stable or improved on treatment in all cases. Total serum protein concentration and alanine aminotransferase and alkaline phosphatase activities fell significantly during treatment. Fourteen dogs were euthanased, four were lost to follow-up and nine remained alive. Mean survival time for the dogs euthanased was 9.9 months. Mean follow-up period for the dogs still alive was 56.9 months and all had survived more than 36 months from diagnosis. Surviving dogs with intrahepatic shunts had a significantly shorter follow-up period than dogs with extrahepatic shunts. Two prognostic indicators were identified, age at initial signs and blood urea concentration on presentation, both correlating with survival time. It was demonstrated that a significant proportion of dogs with portosystemic shunts managed medically have a good prognosis.