The Western Australian Familial Polyposis Registry was established in 1985 by the Cancer Foundation of Western Australia in conjunction with the Health Department of Western Australia. The primary aim of the Registry is the prevention of colorectal cancer in a group of persons at high risk of the disease. Families are notified to the Registry by medical practitioners throughout the State and, at the request of family members and medical practitioners, the project officer for the Registry will arrange for the collection of data, counselling and reminders for follow-up examinations for both cases and family members who are at risk of developing the disease. A total of 44 families with familial adenomatous polyposis is known to the Registry. The crude incidence of polyposis in Western Australia was 0.24 cases per 100,000 persons over the three-year period 1986-1988. The prevalence of the condition in 1988 was 2.59 cases per 100,000 persons. There are 188 family members in Western Australia who are at a 50% risk of developing familial adenomatous polyposis. Registry data indicate that regular follow-up and early treatment reduce the risk of the development of bowel cancer.