Canine gallbladder mucocele (GBM) is an emerging biliary disease in dogs described as the excessive and abnormal accumulation of thick, gelatinous mucus in the lumen, which results in an enlarged gallbladder. GBMs have been diagnosed more frequently in comparison to prior to the 2000s when it was considered rare. The mucus is usually pale yellow to dark green in appearance. The name originates from the Greek word kele meaning tumour as a mucocele resembles a mass. Although this disease is primarily identified in dogs, cats and ferrets have also been diagnosed.