This is a case report of an 8 year old castrated male domestic short hair (DSH) cat who presented to the Cornell University Hospital for Animals’ (CUHA) Internal Medicine service. The patient presented with signs of general malaise, hepatobiliary disease, and respiratory difficulty. Cytology of ultrasound-guided aspirates of multiple liver nodules was used to diagnose mucinous biliary carcinoma as the cause of clinical signs. The patient’s prognosis, based on progression of clinical signs at presentation, was poor to grave. The patient was discharged with palliative therapy and died one and a half weeks later due to respiratory distress. No necropsy was performed. This paper will describe the patient’s clinical presentation, as well as the diagnostic plan, imaging, cytology, and a description of mucinous biliary carcinoma in feline patients.