Colorectal cancer is the second most common form of cancer among women and the third among men in Western countries; about 5-10% of these cancers are of hereditary nature. Familial Adenomatous Polyposis (FAP) is one of these hereditary cancer syndromes. In this thesis a study is described which examines the psychosocial and behavioral impact of FAP on individuals belonging to FAP families in the Netherlands. What is the impact of FAP on FAP-patients, their partners and their relatives? Is there a need for professional psychosocial support? Do patients comply with the advice for colorectal cancer screening? What is the attitude towards having children with the use of reproductive techniques and towards childhood DNA testing? This study aims to answer these questions and gives suggestions for clinical practice and future research