Medical records were reviewed for 18 cats with adenomatous polyps of the proximal portion of the duodenum. Cats of Asian ancestry were over represented (8/18), and male castrated cats were common (15/18). The median age was 11.8 years. Common clinical signs were acute and chronic vomiting and hematemesis. Nine cats were anemic. Contrast radiography was performed in 12 cats, and a mass of the proximal portion of the duodenum was identified in 10 cats. Endoscopy was used to confirm existence of the mass in 3 cats. Complete excision of the duodenal mass was performed in 17 cats. One cat died before abdominal exploratory surgery, and a duodenal adenomatous polyp was identified at necropsy. Fifteen cats survived the immediate postoperative period, with 13 of 15 having complete resolution of clinical signs. Five cats had concurrent disease, which caused 4 of them to die between 3 and 26 months after surgery. Redevelopment of adenomatous polyps was not detected in any cat during the follow-up period of 1 to 49 months. Results of the study indicated that benign, adenomatous polyps of the duodenum in cats can be safely excised and that the prognosis for return to normal function is excellent.