Flexible sigmoidoscopy as a screening procedure in rural patients. In this study of flexible sigmoidoscopy as a screening procedure for rural, impoverished patients, 16% of asymptomatic patients who were screened by sigmoidoscopy and 23% of patients with a positive test for fecal occult blood were found to have a polyp or carcinoma. Flexible sigmoidoscopy appears to be an important part of the physical examination of patients older than 50. It is a test that can readily be done by primary care physicians in a rural setting. 