When a distal common bile duct neoplasm is at the stage of carcinoma in situ or high-grade dysplasia,it is difficult for the surgeon to decide whether to perform pancreaticoduodenectomy.Here we describe a patient with a progressive dysplastic lesion in the common bile duct,which developed from moderate-high to highgrade dysplasia in approximately 2 mo.The patient refused major surgery.Therefore,endoscopic-assisted photodynamic therapy was performed.The result at follow-up using a trans-T-tube choledochoscope showed that the lesion was completely necrotic.This report is the first to describe the successful treatment of highgrade dysplasia of the distal bile duct using photodynamic therapy via a choledochoscope. When a distal common bile duct neoplasm is at the stage of carcinoma in situ or high-grade dysplasia, it is difficult for the surgeon to decide whether to perform pancreaticoduodenectomy. Here we describe a patient with a progressive dysplastic lesion in the common bile duct, which developed from moderate-high to high grade dysplasia in approximately 2 mo. The patient refused major surgery. Beforefore, endoscopic-assisted photodynamic therapy was performed. The result at follow-up using a trans-T-tube choledochoscope showed that the lesion was completely necrotic.This report is the first to describe the successful treatment of highgrade dysplasia of the distal bile duct using photodynamic therapy via a choledochoscope.