Colonic hamartomas are rare polypoid lesions. We report an unusual case of multiple colonic hamartomatous polyps, including a giant hamartoma, unrelated to hereditary or familial polyposis syndromes, in a 48-year-old man. The diameter of the largest polyp was 9.5 cm, and endoscopy revealed that the lesion caused colonic obstruction. The clinical, endoscopic and histological aspects of this case are discussed.