The flexible fiberoptic sigmoidoscope has gained widespread acceptance as a diagnostic tool in the detection and diagnosis of colorectal disease. Since its introduction nearly a decade ago, studies have thus far indicated that in the hands of experienced physicians, flexible sigmoidoscopy is a safe procedure affording greater patient comfort, greater depth of insertion, and a higher yield of neoplastic lesions than rigid sigmoidoscopy, with surprisingly few associated risks. Although reported infrequently, infection is an acknowledged risk of flexible sigmoidoscopy and other endoscopic procedures. The most efficient means of preventing endoscopy-associated infection is uncompromising aseptic practice. Clinical and experimental data obtained from studies designed to investigate endoscopic transmission of infectious organisms and from our own and others' experiences are reviewed. Guidelines for achieving high-level disinfection of the flexible fiberoptic sigmoidoscope are included.