Abstract: Endoscopic retrograde cholangiocretography（ERCP） and routine cytology are general approaches for pre-oprative dignosis of suspected pancreatic duct cancer patients. Routine cytology is with high specificity and low sensitivity. The detection of aneuploidy of 3／7／17 and loss of p16 by fluorescence in situ hybridization（FISH） has revolutionized how laboratories diagnose cholangiocarcinoma and pancreatic adenocarcinoma with increasing sensitivity and minimal decreases in clinical specificity. Although using FISH for diagnostic aim has been more than ten years in foreign， it has not applied to clinical diagnosis in China. Our hospital has promoted this technique and published an article in Chinese Journal of Pathology. However， many peers in other hospitals wonder detailed methods and criterion of this technique， so we provide the information to detect pancreatobiliary cancers in FISH.