Three cases of gallbladder agenesis (GA) have been previously reported in the English-speaking veterinary literature. Affected dogs can be either asymptomatic or symptomatic with vomiting, retching, and anorexia previously reported. The previously reported cases and the dog in this report had marked elevations in alanine aminotransferase concentrations, and liver histopathology consistently showed bridging fibrosis and biliary hyperplasia. The condition is most often diagnosed in humans during exploratory surgery, which was also the case in the previous three dogs reported with GA. Computed tomography (CT) or MRI is now recommended for diagnosis of the condition in humans, and this is the first report of CT findings in an affected dog diagnosed without surgery. Bile stasis and cholangiohepatits have been proposed as secondary pathologies in both humans and dogs with GA, and histopathology and CT findings in this case support those theories.