Idiopathic hepatic fibrosis was diagnosed by liver biopsy in 15 young dogs, of which nine were German shepherds. Clinical signs included ascites, anorexia, weight loss and hepatic encephalopathy. Erythrocyte microcytosis was a consistent clinical feature, and clinical chemistry generally revealed hypoproteinaemia and high serum activities of alkaline phosphatase and, to a smaller extent, alanine aminotransferase. Fasting blood ammonia and serum bile acid concentrations were increased in most dogs examined, and all the dogs tested had prolonged retention of sulfobromophthalein at 30 minutes. Multiple acquired portosystemic shunts were revealed by laparotomy and/or portography. Non-inflammatory fibrosis was present to different degrees in all the dogs' livers, and on the basis of its predominant location these were classified as having central perivenous fibrosis, diffuse pericellular fibrosis or periportal fibrosis. The response to symptomatic treatment and anti-fibrotic therapy with glucocorticosteroids or colchicine was variable. Seven dogs died or were euthanased shortly after diagnosis, but one dog survived two-and-a-half years, and three dogs were still alive more than four years after the initial diagnosis.