Guidelines are presented for the establishment of a regional or national register of patients with familial adenomatous polyposis. The detailed recommendations are based on the work in committees of the "Leeds Castle Polyposis Group" and the "EuroFAP". The aims of national and regional polyposis registers are discussed, and the stages of development of a register are reviewed: Ascertainment of probands, construction of pedigrees, identification of family members at risk, and screening of members at risk. The problem of data confidentiality is discussed.