Familial adenomatous polyposis (FAP) represents a hereditary precancerous condition. Symptoms often appear malignant transformation only. For persons at risk early recognition of gene carriers is essential. Approximately 80% of the patients show congenital hypertrophy of the retinal pigment epithelium (CHRPE) that can be recognized before clinical manifestation of FAP. In order to predict FAP 9 patients and 10 persons at risk from 6 FAP families were examined by endoscopy, molecular genetical and ophthalmological methods. Four patients from two families each had bilaterally 4 CHRPE; four persons at risk did not have CHRPE. This is in accordance with endoscopic and molecular genetic results. The five patients and six persons at risk from the other four families did not have CHRPE, i.e., the percentage of CHRPE in the FAP patients examined was only 45%. Funduscopy permits early identification of gene carriers in families where the FAP patients have CHRPE. CHRPE is not present in persons at risk in these families, it is not necessary to conduct invasive diagnostic measures. Funduscopy should always be done in FAP patients and in persons at risk from CHRPE-positive families. An endoscopic examination should be recommended when CHRPE is observed incidentally in a person with a negative family history for FAP.