Colorectal cancer is the second most common neoplasm and the second most frequent cause of cancer-related deaths in Spain. This neoplasm has an important genetic component, although relatively few of the genes involved in its hereditary or familial forms have been identified. One of the latest genes to be identified is the MYH gene. Colorectal polyposis associated with mutations in the MYH gene is an autosomal recessive syndrome characterized by the development of colorectal adenomas and cancer. It is the first disease predisposing to cancer to be associated with defects in base excision repair.