Aim Lifetime risk of a metachronous colorectal cancer (mCRC) is 0.6-3% following sporadic colorectal cancer (CRC) and 15-26% in Lynch syndrome. The lifetime incidence of CRC in individuals with moderate familial risk is 8-17%. Risk of mCRC is unknown. Method A retrospective longitudinal study of the Regional Familial CRC Registry was performed. Patients who had at least one CRC were categorized as follows: moderate risk (n=383), Lynch syndrome (n=528) and average (population) risk (n=409). The Kaplan-Meier estimate (1-KM) and the cumulative incidence function were used to calculate the risk of mCRC. The 1-KM gives the risk for individuals remaining at risk (alive) at a given time point and thus is useful for counselling. The cumulative incidence function gives the risk for the whole population. Results The 1-KM and the cumulative incidence function demonstrated that the risk of mCRC was significantly higher in moderate-risk patients compared with average (population)-risk patients (1-KM, P=0.008; cumulative incidence function, P=0.00097). However, the risk of mCRC was higher in patients with Lynch syndrome than in moderate-risk or average (population)-risk patients. The 1-KM in moderate-risk patients was 2.7%, 6.3% and 23.5% at 5, 10 and 20years, respectively. In average (population)-risk patients, the 1-KM was 1.3%, 3.1% and 7.0% at 5, 10 and 20years, and the cumulative incidence function was 0.3%, 0.6% and 2.4% at the same time points, respectively. Conclusion These data indicate that the risk of mCRC is significantly higher in patients with a moderate family history of CRC than in those with an average (population) risk. This justifies proactive lifelong surveillance. © 2012 The Association of Coloproctology of Great Britain and Ireland.