Many intraductal papillary-mucinous tumors (IPMTs) have been diagnosed with improvements in diagnostic imaging techniques. The histology of IPMT is various, including hyperplasia to invasive carcinoma. IPMTs are thought to occur multicentrically through the hyperplasia-adenoma-carcinoma sequence. IPMTs are characterized by genetic heterogeneity associated with histologic heterogeneity that may be due to slow growth and favorable prognosis. However, some IPMTs progress to invasive pancreatic cancer through malignant transformation with aggressive clonal progression. Thus some conventional pancreatic cancers may be derived from IPMTs. Although IPMTs and conventional pancreatic cancer initially occur in the ductal epithelium, they are thought to be totally different entities in terms of large or peripheral pancreatic duct origin, developmental style, genetic alterations, and prognosis. In future, differences and/or similarities will be discussed on the basis of molecular analyses of the carcinogensis of both tumors.