Colorectal cancer is one of the most common cancers in the world, with overall mortality exceeding 40% even with treatment. Effective efforts for screening and prevention are most likely to succeed in patient groups identified as high risk for colorectal cancer, most notably the hereditary intestinal polyposis syndromes. In these syndromes, benign polyps develop throughout the intestinal tract prior to the development of colorectal cancer, marking the patient and associated family for precancer diagnosis followed by either close surveillance or preventive treatment.This review article was undertaken to discuss the most recent developments in the knowledge of hereditary intestinal polyposis syndromes, emphasizing the clinical approach to diagnosis and treatment relative to preventing the development of cancer.The most common of the hereditary polyposis syndromes is familial adenomatous polyposis (FAP), which is characterized by the development of hundreds to thousands of adenomatous polyps in the colon followed at an early age by colorectal cancer. Colorectal cancer can be prevented in this autosomal dominant condition by prophylactic colectomy, though a risk for other tumors, including periampullary cancers, remains throughout life. Variant of FAP associated with fewer and smaller polyps (hereditary flat adenoma syndrome), or even CNS tumors (Turcot's syndrome) also carry this high risk of colorectal cancer. Hereditary hamartomatous polyposis syndromes such as juvenile polyposis and Peutz-Jeghers syndrome (also autosomal dominant) are characterized by less frequent polyps. Though these are generally benign polyps, they are also associated with a significant risk of colorectal and other cancers. Other polyposis syndromes, including neurofibromatosis and Cowden's disease, do not carry this increased risk of colorectal cancer, and therefore affect different treatment strategies. Analysis of genetic factors responsible for these and other hereditary syndromes with predisposition to colorectal cancer has not only contributed to our molecular understanding of colorectal cancer, but opened the door to DNA testing and treatment strategies for these diseases.The treatment advances that are discussed and careful screening in appropriate families will effectively reduce the risk of death from colorectal cancer.