Pancreatic intraepithelial neoplasia (PanIN) is a precancerous lesion. A 72-year old man was admitted to our hospital because of abdominal pain, and he had an elevated serum level of pancreatic amylase. ERCP showed a focal stricture of the main pancreatic duct without upstream dilatation in the body of the pancreas. Cytologic evaluation with an endoscopic brush at the stricture suggested the presence of adenocarcinoma. After subtotal pancreatectomy, the features of PanIN were observed in the branch pancreatic duct. ERCP with brush cytology seems to be a useful method for detecting PanIN at the precancerous stage. We report here on a case of PanIN associated with a stricture of the main pancreatic duct.