Background: Anxiety, discomfort, and high levels of concern can affect patient attitude toward endoscopic procedures as well as compliance and adherence to current recommendations for the examination. This study evaluated how patients perceive flexible sigmoidoscopy. Methods: A prospective study was conducted at two sites of 764 patients presenting for GI endoscopy (flexible sigmoidoscopy 175, colonoscopy 384, EGD 205). Before these procedures, patients rated their anticipated (preprocedure) difficulty and degree of concern for each of 30 specific concerns. After the procedure, the patients rated their actual (postprocedure) difficulty. Patients' levels of concerns and difficulty were compared before and after the procedure and among the 3 procedure types. Results: Before the procedure, patients who were to undergo flexible sigmoidoscopy had fewer concerns and lower scores for the severity of the concerns than did patients having colonoscopy or EGD. After the procedure, patients who had flexible sigmoidoscopy rated it as more difficult than patients who had colonoscopy or EGD. Patients who had colonoscopy and EGD graded their actual difficulty as less than their anticipated difficulty. However, patients who had flexible sigmoidoscopy rated the actual difficulty the same as the anticipated difficulty. Conclusions: Although patients have fewer concerns regarding flexible sigmoidoscopy than for the other endoscopic procedures, after the procedure they rate sigmoidoscopy as more difficult compared with postprocedure ratings by patients who underwent colonoscopy or EGD. This suggests that it may be necessary to change the perception of flexible sigmoidoscopy as being the best tolerated of the endoscopic procedures. (Gastrointest Endosc 2002;55:315-20.)