The aim of this study is to improve clinicians' calculation, interpretation and communication of familial colorectal cancer risk, as well as patients' risk perception and uptake of referral for genetic counselling or for surveillance by colonoscopy for their relatives at risk.

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.

Surgeons and gastroenterologists in both the intervention group and the control group will receive background information on familial colorectal cancer risk and the guidelines. Patients and clinicians in the intervention group will receive an additional intervention strategy.

The effect evaluation is done by assessing the number of CRC patients for whom correct risk calculation, interpretation and communication is performed, as well as patients' uptake of the recommended follow up policy. The actual exposure to the different elements of the implementation procedure and the experiences of users will be assessed in the process evaluation. The costs of the implementation procedure will be determined by means of a cost evaluation.

Inclusion Criteria:

• Clinical diagnosis of colorectal cancer before the age of 70
• Diagnosed in one of the participating hospitals
• Able to read and understand Dutch

Exclusion Criteria:

• Previous referral for genetic counseling