The anatomical level reached by the fully inserted flexible sigmoidoscope (60 cm) determines the effective potential of the instrument in the detection of left colon diseases. We performed flexible fiberoptic sigmoidoscopy (FFS) in 50 patients, without the help of fluoroscopy and without trying to reduce the bendings of the sigmoid colon. After having inserted the instrument, the endoscopist would define the section reached: sigma, sigmoid-descending colon junction, descending colon, splenic flexure. Barium sulphate was then injected through the fiberoptic sigmoidoscope in order to verify the level: the exact anatomical localization of the tip of the instrument was therefore determined by means of fluoroscopy. 90% of the investigations visualized the whole sigmoid colon, and in 52% more than 50% of the descending colon was studied; the splenic flexure was reached in only 22% of cases. Worse results, i.e. the visualization of only the sigmoid colon, were achieved in old and overweight patients, who had previously undergone abdominal or pelvic surgery. The paper concludes underlining the great diagnostic potential of FFS in the screening and early diagnosis of left colon diseases. FFS should become the surgeon’s first instrumental investigation even in his own surgery, as the technique is easy to perform, fairly inexpensive and requires simple preparatio