An 11 yr old female neutered domestic shorthair presented for an 8 mo history of an asymptomatic abdominal mass. Computed tomography described an irregular, cystic structure closely associated with the duodenum, and focal ultrasonography confirmed the mass shared outer layers with the intestinal wall. Coeliotomy revealed the mass was originating from, and firmly adhered to, the antimesenteric border of the duodenum but was not communicating with the intestinal lumen. En bloc mass resection with omentalization was performed without small intestinal resection. Histopathology confirmed an enteric duplication cyst. The cat made a full recovery and remained asymptomatic postoperatively with no evidence of recurrence. A review of the literature confirms the duodenum to be the most common location of enteric duplication cysts in felines and that subtotal excision is curative in most cases. This differential should be considered in cases of cystic gastrointestinal structures in juvenile and adult felines, with or without associated clinical signs. In cases of luminal involvement or malignant transformation, intestinal resection and anastomosis is more appropriate. This report describes the presentation, investigations, and treatment of an asymptomatic duodenal duplication cyst in an adult feline and summarizes and compares current knowledge of the condition between veterinary and human literature.