Congenital gallbladder agenesis is an extremely rare disorder, which has, to the best of our knowledge, only been reported in seventeen dogs (mainly in Japan). In almost all of these cases, gallbladder agenesis or hypoplasia was detected in small dogs. In this report, we present a case of gallbladder agenesis in a 9-month-old intact female Bull Terrier. The clinical signs included diarrhoea, sporadic vomiting, apathy and decreased appetite. The serum biochemistry revealed an increased liver enzyme activity, an increased concentration of serum bile acids and mild hyperbilirubinaemia. A diagnostic laparotomy demonstrated the lack of a gallbladder and dilation of the common bile duct, which was misinterpreted as the gallbladder in the ultrasonographic examination. The histological examination of the liver revealed degenerative changes in the hepatocytes with glycogen accumulation and some necrotic hepatocytes. The therapy included a low protein diet, fluids, silymarin and ursodeoxycholic acid. After nine weeks of therapy, the dog was in good condition, the diarrhoea and vomiting ceased, and the liver function parameters, such as the AST and GLDH activities, and the concentration of bile acids had decreased to reference intervals.