Background and Study Aims: Colonoscopy without sedation costs less than sedated colonoscopy. The aims of the present study were to determine the percentage of patients who can successfully undergo nonsedated colonoscopy and to identify factors capable of predicting whether a colonoscopy can be completed without sedation. Patients and Methods: Demographic, clinical, and colonoscopy-related data were prospectively recorded for consecutive patients undergoing colonoscopy by an experienced endoscopist in a single private practice setting. All of the colonoscopies routinely began without sedation, unless sedation was specifically requested by the patient. Sedation was given when requested by the patient if significant discomfort occurred during the procedure. To determine factors making it more likely that nonsedated colonoscopy would be possible, age, sex, presence of diverticulosis, prior colonic surgery, prior colonoscopy, and the time required to complete the colonoscopy were evaluated using a multivariate logistic regression analysis. Results: Five patients asked to have sedation before the procedure. Of 173 patients in whom colonoscopy was started without sedation, 159 (91.9 %) required no sedation. Complete colonoscopy was achieved in 152 of the 173 initially nonsedated patients (87.9 %) and in 167 of the total of 178 patients (93.8 %). Multivariate logistic regression analysis showed that male sex (odds ratio 5.9; 95 % CI, 1.7 to 21.4) and a prior segmental colonic resection (odds ratio 6.2; 95 % CI, 0.8 to 48.9) were associated with an ability to complete the colonoscopy procedure without sedation. Conclusions: The vast majority of patients undergoing colonoscopy procedures conducted by an experienced endoscopist do not require sedation. Male sex, segmental colonic resection, and probably experience in lower gastrointestinal endoscopy on the part of the patient, are predictive factors for successful colonoscopy without sedation.