Regular colonoscopy is effective in reducing morbidity and mortality due to colorectal cancer (CRC) in patients at increased familial CRC risk. Currently, the majority of these at-risk individuals are not properly referred for increased surveillance by colonoscopy or genetic counselling. In 2008, a national multidisciplinary evidence-based guideline on familial and hereditary CRC was launched in the Netherlands. Clinicians have new tasks in familial CRC risk calculation, interpretation and communication. A clustered randomized controlled trial including an effect, process and cost evaluation will be conducted in eighteen Dutch hospitals to determine the most cost effective way to implement these new guidelines.