We have previously demonstrated that we could improve colonoscopic surveillance practice for patients at increased risk of colorectal cancer by the adoption of guidelines, facilitated by a nurse co-ordinator. This study was to determine whether we could sustain this improvement over a longer period (4 years). All colonoscopic surveillance decisions made by the co-ordinated colorectal screening programme of our hospital between 2000 and April 2004 were reviewed. Reasons for variance were recorded, and surveillance decisions made in the last 4 months of the study time were compared with decisions made 4 years previously, both before and after the introduction of the co-ordinated programme. Between 2000 and 2004, 1794 surveillance decisions were made with variance occurring in 100. In the last 4 months of the period of study, 98% of decisions matched guidelines, suggesting that the improvement made following the adoption of the guidelines (45-96% p < 0.05) could be maintained. Reasons for variance from guidelines included a belief that the particular clinical scenario was not covered in the guidelines, disagreement with the guidelines or patient anxiety. Adherence to evidence based medicine guidelines for colonoscopy surveillance can be maintained over time at a high level. A number of clinical scenarios are not covered adequately by the existing guidelines and continue to generate disagreement amongst clinicians.