The purpose of the study was to investigate the anatomic location of the flexible rectosigmoidoscope (60 cm) when introduced as far as technically possible. One hundred and forty-nine consecutive patients referred for double-contrast enema (DCE) were examined with rectosigmoidoscopy before the radiologic examination, and CO2 was used for insufflation. A plain abdominal film was taken to locate the tip of the instrument when 60 cm or as much as possible of the instrument had been introduced. The sigmoid loop was passed and the tip of the scope located in the ascending colon or at the left flexure in 99 (66%) of the patients, and in a further 27 (18%) the upper part of the sigmoid colon was reached. The sigmoid colon had been passed in 71%, 80%, and 44% when 60, 50, and 40 cm of the instrument was introduced, respectively. DCE could be performed at the same session as the rectosigmoidoscopy, as CO2 was quickly absorbed. In the vast majority of patients the sigmoid colon can be inspected with a rectosigmoidoscope.