Background: Regular colonic surveillance of familial adenomatous polyposis (FAP) patients is necessary to ensure appropriate prophylactic surgery is performed before colorectal cancer (CRC) develops. Polyposis Registries have been established to coordinate screening programmes. The aim of this study was to assess the effect of screening and of the formation of the Registry on survival, incidence of CRC and age at onset of CRC, in FAP patients. Methods: Patients on the Manchester Polyposis Registry were categorised according to their mode of presentation; screening or symptomatic, and survival time from birth was calculated for each patient (n=353). The effect of the formation of the Registry was assessed by comparing survival times from birth for patients diagnosed in the 20 years before the establishment of the Registry, to patients diagnosed in the 20 years since the formation of the Registry (n=273). Results: This study demonstrated that survival was increased from 57.8 years to 70.4 years (p<0.001) by screening, and from 58.1 years to 69.6 years (p=0.007) following establishment of the Polyposis Registry. The incidence of CRC was reduced from 43.5% to 3.8% by screening, and from 28.7% to 14.0% following establishment of the Polyposis Registry. Although direct causation between improved survival and reduced CRC incidence, and establishment of the Registry cannot be proven, an association has been demonstrated. Colorectal cancer was found to develop, on average, 16 years later in the screening population. Conclusion: A regular systematic large bowel screening programme, managed by a Polyposis Registry, significantly improves the prognosis of FAP.