In order to enable consequent screening in at risk persons and life-long follow-up in patients, a computer-based polyposis registry was initiated in 1991. It now includes data of 130 FAP patients and 179 risk persons from 87 families, that were seen in our clinic since 1982. 20.5% of the "probands" (symptomatic patients) had a colorectal carcinoma at the time of diagnosis in contrast to none in the "call-up" group. The most reliable screening method as yet has proven to be the flexible sigmoidoscopy with histological verification of the adenomatous nature of the polyps. Congenital hypertrophy of the retinal pigment epithelium was only seen in 50% of our patients. The exact localisation of the FAP gene in August 1991 will soon significantly improve the prognostic value of molecular genetic screening procedures. The improved prognostic value of the method will enable early and even prenatal diagnosis. It will not any more be necessary to wait for the phenotypic manifestation (colorectal polyps) in order to be sure of the diagnosis FAP.