Familial adenomatous polyposis is a dominant hereditary disease which includes early development of up to several thousand colorectal adenomas and subsequent development of colorectal adenocarcinoma in all of the untreated cases. In addition, various extracolonic manifestations may be observed. These include epidermoid cysts, osteomas, desmoids and gastroduodenal polyps. Conventional proctosigmoidoscopy is employed as the primary diagnostic method as all of the patients have rectal adenomata. Thereafter colonoscopic examination is undertaken and gastroduodenoscopy is performed on account of the risk of development of duodenal adenomas. Treatment consists of prophylactic colectomy at about the age of 15 years. An ileorectal anastomosis is most frequently made but construction of an ileoanal reservoir may be considered in selected cases. Regular prophylactic control examinations of first degree relatives of affected family members should commence at the age of ten years. Recent demonstration of a specific gene for polyposis on chromosome 5 will, together with demonstration of retinal pigmentation permit early preclinical diagnosis in future. Establishment of the Polyposis Register has resulted in earlier tracing and treatment of the condition and an improved prognosis.