Background: Colonic hamartomas are uncommon in adults. The aims of this study were to determine (1) the prevalence of colonic hamartomas in an adult populatio n undergoing colonoscopy and (2) the clinical, endoscopic, and histologic featur es of colonic hamartomas in adult patients. Methods: A pathology database identi fied 19 adult patients of 12,707 patients with colonic hamartomas in the 11-yea r study period from January 1992 to October 2002. An endoscopic computer databas e provided information about the number of colonoscopies performed and the prese nce or the absence of colonic polyp(s) in study patients. Charts of patients wit h colonic hamartomas were reviewed, and clinical and demographic data were colla ted. Results: Nineteen patients were found to have colonic hamartomas. The mean age of these patients was 55 years, with an age distribution ranging from 25 to 81 years. The prevalence of colonic hamartomas in this study population was 0.15 %. The prevalence of hamartomas in patients with colon polyps at index colonosc opy was 0.073%. Colonic hamartomas were more common in men than in women. The i ndication for colonoscopy for the majority (68%) of patients was hematochezia o r the presence of occult blood in the stool. Three fourths of the polyps were gr eater than 1 cm in diameter, and 89%were pedunculated. Two thirds of the hamart omatous polyps were localized to the rectosigmoid region. Endoscopic characteris tics of hamartomas were indistinguishable from adenomas. Conclusions: Colonic ha martomas in adults are rare. They tend to be single, pedunculated, and localized predominantly in the rectosigmoid region. Endoscopic resection of colonic hamar tomas was successful in all patients. Background: Colonic hamartomas are uncommon in adults. The aims of this study were to determine (1) the prevalence of colonic hamartomas in an adult populatio n undergoing colonoscopy and (2) the clinical, endoscopic, and histologic featur es of colonic hamartomas in adult patients. Methods: A pathology database identi fied 19 adult patients of 12,707 patients with colonic hamartomas in the 11-yea r study period from January 1992 to October 2002. An endoscopic computer databas e provided information about the number of colonoscopies performed and the prese nce or the absence of colonic polyp (s) in study patients. Charts of patients wit h colonic hamartomas were reviewed, and clinical and demographic data were colla ted. Results: Nineteen patients were found to have colonic hamartomas. The mean age of these patients was 55 years, with an age distribution ranging from 25 to 81 years. The prevalence of colonic hamartomas in this study population was 0.15%. The prevalence of hamartomas in patients with colon polyps at index colonosc opy was 0.073%. Colonic hamartomas were more common in men than in women. The i ndication for colonoscopy for the majority (68%) of patients was hematochezia or the presence of occult blood in the stool. Three fourths of the polyps were gr eater than 1 cm in diameter, and 89% were pedunculated. Two thirds of the hamart omatous polyps were localized to the rectosigmoid region. Endoscopic characteris tics of hamartomas were indistinguishable from adenomas. Conclusions: Colonic ha martomas in adults are rare. They tend to be single, pedunculated, and localized predominantly in the rectosigmoid region. Endoscopic resection of colonic hamar tomas was successful in all patients.