Introduction: A juvenile polyp, also referred to as a congenital polyp, retention polyp,or juvenile adenoma, is a type of hamartoma that is found most commonly in asymptomatic pediatric patients (1% of the under-10 population) and very rarely in adults. Its main symptom is rectal bleeding. Boys are more frequently affected than girls. Juvenile polyp occurs predominantly in the distal colon, with over 90% of cases detected within 20 cm of the anal verge. In South Korea, there have been reports on juvenile polyposis, but not many cases have been reported to date. Here we report a rare case of a rectal juvenile polyp detected in an adult that was mistaken for a malignant tumor. Case: A 23-year-old man of foreign nationality without any signifi cant personal or family medical history presented to our hospital for sporadic bloody stools over the past 2 years. Colonoscopy revealed a single red pedunculated polyp with a 2-cm diameter at a distance of 20 cm from the anal verge. Its surface was round, smooth, red, and eroded. Suspected to be a common adenomatous polyp, it was removed by snare polypectomy. The subsequent histologic examination confi rmed its identity as a juvenile polyp, and the bloody stools improved. Conclusion: A polyp detected in the colon requires histological examination via polypectomy, and given the reported cases in which a juvenile polyp progressed to a precancerous lesion, albeit very rare, close follow-up observation is necessary.