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Chronic liver diseases are common in dogs, however, their causes are often undetermined. They have been associated with long-term phenobarbital therapy, used in large-scale as anticonvulsivant drug in small animal clinics. In the investigation of etiology for liver disease in dogs it’s important to check the prolonged use of phenobarbital. A retrospective study of canine necropsies performed at Laboratory of Veterinary Pathology of Universidade Federal do Rio Grande do Sul, was made from 2000 to 2010, and two cases of chronic diffuse hepatopathy in dogs under phenobarbital therapy (more than six months of treatment) were diagnosed. The main macroscopic findings, such as smaller, firmer and irregular surface of liver, ascites and other sites edema, and portosystemic shunts were observed. Histologically, the most important lesions were observed in the liver. There were diffuse fibrosis, bile ducts proliferation, mononuclear inflammatory infiltrate, cholestasis, and, in one case also occurred regenerating nodules of hepatocytes with vacuolization of hepatocytes cytoplasm. The diagnosis of chronic hepatopathy was based on these findings, and the intensity of the injuries was consistent with the time of treatment using phenobarbital.