Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 11 2 2026 08 29 71 75 Abbas Ahmadifar Gastrointestinal and Hepatobiliary Research Center, Isfahan University of Medical Sciences, Isfahan, Iran. Hoda Imani Department of Adult Gastroenterology and Liver Diseases‚ Isfahan University of Medical Sciences‚ Isfahan‚ Iran. 2026 05 13 2026 06 29 Retention polyps, also known as juvenile polyps, are non-neoplastic hamartomatous lesions. Their occurrence in adults is rare, and finding a solitary retention polyp in a patient with underlying inflammatory bowel disease (IBD) is exceptionally uncommon. We report the case of a 42-year-old male with a 9-year history of ulcerative colitis, currently in clinical and endoscopic remission (Mayo Endoscopic Score 1) on mesalamine therapy. During a routine surveillance colonoscopy, a solitary, asymptomatic, 15 mm sessile polyp with a smooth, cystic appearance was discovered in the rectum. The lesion was removed via endoscopic mucosal resection (EMR). Histopathological evaluation revealed no evidence of dysplasia or malignancy, confirming the diagnosis of a retention polyp. Although rare, retention polyps should be considered in the differential diagnosis of solitary polyps in adult patients with UC. Complete endoscopic resection and precise histopathological examination are essential to rule out dysplasia and guide appropriate management. https://crcp.tums.ac.ir/index.php/crcp/article/view/1188 https://crcp.tums.ac.ir/index.php/crcp/article/download/1188/782