A 14.5 year old castrated male Shetland Sheepdog presented to the Cornell University Hospital for Animals’ Internal Medicine Service for further evaluation and treatment for a previously diagnosed gallbladder mucocele (GBM). The patient was asymptomatic at the time of presentation despite his advanced disease. This case serves as a model to discuss the common clinical presentation and signalment of patients with GBM as well as their diagnosis, treatment, and prognosis. Although the pathogenesis is not completely understood, there is believed to be a link to primary or secondary dysmotility of the gallbladder. Similarly, no definitive underlying etiology has been identified, but dyslipidemias and endocrinopathies appear to have a strong association with the development of a GBM. GBM are being diagnosed with increasing frequency in veterinary medicine and warrant further clinical investigation.