A cyst of the common bile duct (CBD) is reported in a 9-year-old cat that presented with a 1-week history of anorexia, weight loss and vomiting. Diagnosis was established by ultrasound examination and laparotomy, and was ultimately confirmed by histological analysis. Chronic cholangitis and an Escherichia coli species were detected concurrently according to the histopathological findings and bile culture, respectively. The case was managed by suturing the borders of the ostium of the cyst over a stent, using a temporary cholecystostomy tube and antibiotic therapy. At 7 months following the surgery, the cat was in excellent physical condition with no clinical evidence of recurrence of cholangitis or of the cyst after ultrasonographic evaluation. According to the human literature, cysts of the CBD require treatment because of their common association with cholangitis, pancreatitis, and cystic rupture. We were unable to confirm a link between the cyst and cholangitis in this case. It is possible that detection of this anomaly was an incidental finding unrelated to bacterbilia. Histological examination of cyst tissue is mandatory for a definitive diagnosis and to differentiate it from neoplasia. This is the first description of a cyst of the CBD in the cat.