AbstractIntraductal papillary neoplasms of the bile duct (IPNBs) are papillary epithelial proliferations with delicate fibrovascular cores within dilated bile ducts. They are thought to be premalignant lesions with potential to progress invasive tumors. To our knowledge, there are no prior descriptions of IPNB cytomorphology. A 58‐year‐old male presented with painless jaundice and elevated liver function tests was found to have an intraluminal mass within the left hepatic duct. A bile duct brushing diagnosed as “atypical cells present” showed a cellular specimen composed of papillary groups and linear strips of mostly cuboidal/columnar cells with mild atypia and vacuolated cytoplasm. A left hepatic lobectomy including extrahepatic bile ducts showed the mass consisted of papillary cores lined by pancreatobiliary‐type epithelium with mild‐to‐severe atypia, consistent with IPNB with a focus suspicious for invasion. The cytomorphologic features described in the current case suggest intraductal papillary neoplasm but may not be specific since similar features could be seen in other bile duct tumors and even in nonneoplastic conditions such as stent or cholelithiasis. However, it is worthwhile to report papillary hyperplasia with atypia in common bile duct brushings in order to avoid a false‐negative diagnosis, especially in the context of a filling defect by images which does not appear to be a stone.