BACKGROUND Endoscopic sphincterotomy is an established treatment for common bile duct stones. Stone impaction at the ampulla makes deep cannulation and standard sphincterotomy more difficult. The use of precut papillotomy may facilitate stone extraction, although risks may be greater. OBJECTIVE To evaluate precut papillotomy in impacted common bile duct stone at the ampulla of Vater. METHODS Between October 1990 and September 1995, 27 of 345 patients with common bile duct stones underwent needle knife precut papillotomy after conventional sphincterotomy failed due to impacted ampullary stone. This facilitated deep cannulation and subsequent standard sphincterotomy in 12 patients. RESULTS Eleven patients had spontaneous expulsion of the stone when precut papillotomy was extended. Oedema or bleeding precluded stone extraction in 3 patients, and these stones were removed at a second endoscopic retrograde cholangiopancreatography (ERCP) session. Mild bleeding occurred in one patient and hemotransfusion was necessary. There was no perforation or pancreatitis following the procedure. CONCLUSIONS Precut papillotomy is effective in the treatment of impacted common bile duct stone at the ampulla of Vater. It's a technique that should be performed only by an experienced endoscopist and does not increase the complications risk.