© 2015 The Association of Coloproctology of Great Britain and Ireland. Aim: Colonic surveillance reduces the lifetime risk of colorectal cancer in patients with Lynch syndrome (hereditary nonpolyposis colorectal cancer) from 60 to 80% to 10% and confers a 7-year survival advantage. The British Society of Gastroenterologists recommends colonoscopy at least every 2 years from the age of 25. Currently in the UK, genetic diagnosis is made by a regional genetics service, and screening recommendations are made to the referring clinician. The aim of this study was to investigate compliance with and the effectiveness of large bowel surveillance in Lynch syndrome. Method: A retrospective longitudinal study of Lynch syndrome mutation carriers on the Regional Familial Colorectal Cancer Registry under and not under screening was conducted. To investigate screening compliance, patients were included if they were alive at the start of the study. Data were gathered on timeliness, quality and outcome of screening. To examine the effectiveness of screening, the cumulative incidence of colorectal cancer was estimated using Kaplan-Meier curves and the screened population compared with patients not being screened. Results: A total of 227 Lynch syndrome mutation carriers were under screening at 26 hospitals. We assessed 439 colonoscopies for timeliness, of which 68% were compliant (interval < 27 months). Compliance on the 1 November 2011 was 87%. The cumulative incidence of colorectal cancer to the age of 70 was 25% (95% CI 17-32%) in the surveillance population and 81% (95% CI 78-84%) in 689 mutation-positive patients not being screened (P < 0.0001). Conclusion: Overall, 68% of colonoscopies were on time. The incidence of colorectal cancer was greatly reduced by screening but remained significant. Patients with Lynch syndrome need proactive surveillance management.