In a prospective study, the complications observed in 242 consecutive patients after endoscopic sphincterotomy for common bile duct stones were recorded over a period of up to three months. Patients with previous gastric surgery, papillotomy, or additional pancreato-biliary disease other than gallbladder stones were excluded. The overall complication rate was 14%, 74% of these complications being moderate or severe. The complication rate due to cholangitis was higher in (1) the group with retained stones following complete papillotomy and without biliary drainage, and (2) the group with failed precut papillotomy and drainage after cholangiography, both compared to patients with successful drainage (75% vs. 2.6%: p < 0.001 and 40% vs. 2.6%: p = 0.001 respectively). Both pancreatitis and retroperitoneal air leakage occurred in 1.7% of cases. They were more frequently observed in patients with a smaller diameter (< 10 mm) in the distal common bile duct (5.6% vs. 0%: p = 0.007 for pancreatitis, and 2.8% vs. 1.2%; n.s. for perforation) and especially following precut papillotomy (13.0% for pancreatitis and 8.7% for perforation), which had to be performed more often in these patients. Bleeding following sphincterotomy was relatively frequent when the papilla was located at the lower rim of or inside a diverticulum, compared to patients without a diverticulum (16.2% vs. 2.7%: p = 0.004 and 26.7% vs. 2.7%: p < 0.001 respectively). When the papilla was located inside diverticula, both the rate of perforation and bleeding increased following precut papillotomy, compared with standard papillotomy only (33% vs. 0%, n.s., and 33% vs. 22%, n.s.).(ABSTRACT TRUNCATED AT 250 WORDS)