The polyposis syndromes have been categorized according to polyp histology and clinical phenotype. The clinical importance of the syndromes relates to their inheritance as well as to their benign and malignant manifestations. Familial adenomatous polyposis (FAP) is the most common and best characterized of the polyposis syndromes. Genetic and molecular mechanisms for the phenotype of attenuated FAP (AFAP) continue to be identified, including adenomatous polyposis coli (APC) mosaicism, whole gene deletion, large gene rearrangements, multiple APC mutations, and MUTYH gene mutations. The phenotype of AFAP or MUTYH‐associated polyposis (MAP) is also associated with POLE and POLD1 genes. Patients with MAP have a reasonable chance of meeting criteria for serrated polyposis syndrome (SPS), although it is uncommon for patients with SPS to have biallelic MUTYH mutations. Neural elements can be observed in the juvenile polyps of cowden syndrome (CS) and BSS, and when found, are somewhat distinctive for those diagnoses.