Diagnostic and therapeutic endoscopic retrograde cholangiopancreatography (ERCP/ES) can be associated with unforeseeable complications, especially when involving postprocedural pancreatitis. The aim of the study was to investigate risk factors for complications of ERCP/ES in a prospective multicentric study. One hundred fifty variables were prospectively collected at time of ERCP/ES and before hospital discharge over 2 years, in consecutive patients undergoing the procedure in nine endoscopic units in the Lombardy region of Italy. More than 150 ERCPs were performed in each center per year by a single operator or by a team of no more than three endoscopists. Two thousand four hundred sixty-two procedures were performed; 18 patients were discharged because the papilla of Vater was not reached (duodenal obstruction, previous gastrectomy, etc.). Two thousand four hundred forty-four procedures were considered in 2103 patients. Overall complications occurred in 121 patients (4.95% of cases): pancreatitis in 44 patients (1.8%), hemorrhage in 30 (1.13%), cholangitis in 14 (0.57%), perforation during ES in 14 (0.57%), and others in 14 (0.57%); deaths occurred in three patients (0.12%). In multivariate analysis, the following were significant risk factors: a) for pancreatitis, age (< or = 60 yr), use of precutting technique, and failed clearing of biliary stones, and b) for hemorrhage, precut sphincterotomy and obstruction of the orifice of the papilla of Vater. The results of our study further contribute to the assessment of risk factors for complications related to ERCP/ES. It is crucial to identify high risk patients to reduce complications of the procedures.