Once upon a time, there was only one syndrome of polyposis … familial adenomatous polyposis. Those were the good old days when ignorance was bliss. Now the clinical geneticists have staged a determined effort to uncover any genetic abnormality that can cause multiple premalignant polyps, and so now we have to know about MUTYH-associated polyposis, NTHL1-associated polyposis, polymerase proofreading polyposis, and sessile serrated polyposis, not to mention colonic polyposis of unknown etiology (CPUE) and MSH3-associated polyposis. MUTYH-associated polyposis (MAP) was one of the first syndromes discovered during the “genomic era,” as it was found by investigating the genes that could possibly cause a GC:TA transversion in a tumor. This led investigators to the genes controlling base excision repair, the way the body repairs oxidative damage to the DNA. This chapter describes clinical features of MAP.