Background. Successful colonoscopy depends on insertion of the instrument to the cecum, precise observation, and minimal patient discomfort during the procedure. This prospective study was designed to identify factors, apart from the endoscopist's skill, that predict patient pain and technical difficulty during sedation-free colonoscopy. Methods. A total of 426 sedation-free colonoscopies performed by one experienced endoscopist were evaluated in a prospective manner. Factors were recorded. including patient pain level, intubation time, demographic data, history of abdominal surgery, bowel preparation status. diverticular disease, bowel habits, anxiety level, and number of previous colonoscopies. These factors were analysed to determine their association with difficulty and pain during the procedure. Results. Four hundred six colonoscopies were completed to the cecum (95.3%). Mean insertion time for complete colonoscopy was 6.5 +/- 3.5 min. Multivariate logistic regression analyses revealed that older age, lower body mass index, previous hysterectomy, diarrhoea, 1st time colonoscopy and anxiety were predictors of patient pain. Older age, lower body mass index and previous hysterectomy were predictors of difficulty of intubation. Conclusions. This prospective Study identified several factors that may predict patient pain and technical difficulty associated with the procedure. These findings have implications for the practice and teaching of colonoscopy. (c) 2007 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.