Background/Aims: It is sometimes difficult to incise the distal papillary roof (PR) completely in patients with choledocholiths and choledochoduodenal fistula (CDF). The Iso-Tome® (MTW-Endoskopie W. Haag KG), which is helpful in preventing electrical leakage, has good orientation capabilities and can be easily placed at the orifice of the CDF or ampulla of Vater (AV). We aimed to evaluate the efficacy of endoscopic sphincterotomy (ES) with the Iso-Tome® for cutting the distal PR. Methods: Between May 2003 and July 2012, 35 patients were analyzed retrospectively. The distal PR was cut downward and/or upward using the Iso-tome® until the pink intrapapillary mucosa was fully exposed. Downward incisions were performed from the opening of the CDF to the orifice of the AV; upward incisions were performed in reverse. Results: Spontaneous or artificial CDF occurred in four and 31 patients, respectively. The technical and therapeutic success rates were 94.3% (33/35) and 94.3% (33/35), respectively. There was no case of electrical damage to the pink intrapapillary mucosa. Adverse events occurred in 2.9% (1/35; 1, mild bleeding) of patients. Conclusions: The new technique of ES with the Iso-tome® is feasible and useful for effectively incising the distal PR in patients with CDF and choledocholiths. (Gut Liver, 2015;9:231-238)