Secondary prevention is undoubtedly a vital consideration in the early diagnosis of cancer of the large bowel. The examination of asymptomatic subjects considered to be at high risk of colorectal carcinomas will improve the prognosis for this tumour by identifying lesions at an early stage or, even better, pathologies considered precancerous. Rectosigmoidoscopy was therefore employed on a sample of asymptomatic geriatrics, at high risk because of their age. The examination of 245 elderly people revealed various asymptomatic conditions (haemorrhoids, rhagades, polyps, etc.) and, more importantly, 4 cases (1.6%) of rectosigmoid tumours, 2 of them Dukes stage A and 2 polyps in the initial phase of degeneration into malignancy. The paper concludes by emphasising the value of mass screening of the elderly and indeed of other high risk groups using a flexible rectosigmoidoscope, in the hope of identifying early-stage tumours or precancerous lesions with a view to reducing the incidence of colorectal carcinoma and therefore significantly improving the prognosis for that condition.