PURPOSE: To evaluate US, CT and endoscopic retrograde pancreatography (ERP) findings of intraductal mucin-hypersecreting neoplasm (IMHN). MATERIALS AND METHODS: We categorized an IMHN as belonging to a group of disease that can be clinically detected by the pooling of mucus produced by tumors inside the main duct or branch ducts of the pancreas, thus causing dilatation of these ducts. We retrospectively reviewed the US, CT and ERP findings of five patients (hyperplasia, 4; adenocarcinoma, 1). RESULTS: On US and/or CT, diffuse dilatation of the main pancreatic duct was demonstrated in five patients. In two cystic lesions corresponding to cystic dilatation of branch ducts were noted at the pancreatic head (n=1) and neck (n=1). In one patient, multiple cystic lesions were seen on CT along the entire pancreas, but these were not detected on US. In all patients, dilatation of the main duct and/or its branch ducts was seen on ERP. Filling defects resulting from mucin in the main duct or branch ducts were noted in all cases. Lymphadenopathy was not seen on US or CT, but carcinoma peritonei was found in the adenocarcinoma patient at the time of operation. CONCLUSION: IMHN usually shows smooth, diffuse dilatation of the main duct, and on US or CT, dilated branch ducts are occasionally noted. ERP findings are the most characteristic and conclusive; dilatation of the main duct and/or branch ducts is noted, with a filling defect corresponding to mucin. If overlooked during diagnosis, an IMHN might be interpreted simply as chronic pancreatitis, and so the recognition of this neoplasm is important.