Invasive ductal adenocarcinoma (IDA) of the pancreas (IDAP) originating from the ductal gland has a poor prognosis. Noninvasive carcinomas are principally intraductal papillary mucinous carcinomas (IPMCs) and pancreatic intraepithelial neoplasms 3 (PanIN-3). Small papillary-cohesive clusters, individually well-enveloped nuclei in well-preserved cytoplasm, centrally located nuclei, small nuclei (about 10 mum), euchromatin, clearly defined cell borders, small cytoplasm without prominent anisocytosis and no cytoplasm more than 21 mum in shortest diameter, a mixture of goblet cells, and a pleomorphic aspect are common in IPMC and intraductal papillary mucinous neoplasm (IPMN), whereas malignancy in nuclei are observed only in IPMC. PanIN-3 cells have small papillary-cohesive and compact clusters, a monomorphic aspect, and small dense cytoplasm and are highly suggestive of malignancy. IDA cells have loose sheet and solid clusters, poorly preserved cytoplasm, nuclei that tend to adhere to each other, large nuclei, a combination of large nuclei (short diameter <15 mum) with hyperchromatin, a monomorphic aspect, and abundant cytoplasm more than 21 mum in the shortest diameter. To preoperatively differentiate noninvasive IPMC and PanIN-3 from IDAP, these features would be clinically very useful.