Germline mutations of the Adenomatous polyposis gene (APC) are responsible for Familial Adenomatous Polyposis (FAP), an inherited condition that predisposes to the development of hundreds to thousands benign adenomas in the colo-rectum. If not surgically removed, they inevitably progress into malignant adenocarcinoma. To date more than 450 germline mutations have been described allowing the establishment of genotype/phenotype correlation between the site and type of molecular defects and their morbid consequences. Authors reviewed their experience concerning 22 FAP affected patients and their 26 first degree relatives, in whom the mutational analysis of the APC gene had been carried out. Site and type of mutations were associated with clinical parameters (age of onset, rectal involvement, extracolonic manifestations, presence of colorectal cancer) and treatments. The impact of mutational analyses on the clinical approach could be very interesting in the future, modifying both surveillance programs and therapeutical choices.