AIM OF THE STUDY: Amongst family members at risk of developing familial adenomatous polyposis (FAP) to distinguish between those who are affected by the disease and those who are not, in order to provide optimal treatment to those requiring it whilst excluding those without the disease from the endoscopic surveillance programme. MATERIAL AND METHODS: A programme of endoscopy, ophthalmologic examination for retinal pigment lesions associated with FAP and genetic analysis was proposed to a patient suffering from FAP and 3 of his children considered to be at risk. RESULTS: One person at risk eventually proved to have the disease. He had diffuse recto-colic polyposis as well as the typical retinal lesions found in his father and was treated by prophylactic proctocolectomy. He had inherited the mutated paternal allele. The other 2 children had neither polyposis nor retinal lesions and had inherited the normal allele from their father. DISCUSSION: Retinal lesions seen at fundoscopy allowed the diagnosis of FAP to be made before endoscopic confirmation in one patient at risk for FAP, but their absence did not exclude the diagnosis in the other 2. In these patients genetic analysis revealed that they had inherited the normal paternal allele and hence would not develop FAP. CONCLUSION: Systematic investigation of a family suffering from FAP allowed the members at risk to be identified. Two subjects at risk were able to be excluded from further follow-up and the remaining patient was able to be treated in an optimal fashion. An algorithm is proposed for the screening of patients at risk.