The laminin-5-gamma-2 chain is expressed in various invasive carcinoma cells. To clarify the relationship between laminin-5 expression and the development of intraductal papillary-mucinous tumors (IPMTs), we performed an immunohistochemical study of 26 IPMTs and 30 invasive ductal adenocarcinomas. Cases were classified into five groups: intraductal papillary-mucinous adenoma (Group A; n = 8), adenocarcinoma without invasion (Group B; n = 3), adenocarcinoma with minimal invasion (Group C; n = 5), adenocarcinoma with macroscopically evident invasion (Group D; n = 10), and invasive ductal adenocarcinoma (conventional type; Group E; n = 30). In the invasive components of Groups D and E, laminin-5 was expressed in 80% and 100% of cases, respectively. In the intraductal components of IPMTs, expression of laminin-5 was not seen in Groups A and B, whereas they were seen in one case in Group C (20%) and in seven in Group D (70%). Most of the staining patterns of the intraductal components were focal and scattered. Laminin-5-gamma-2 expression in the intraductal components of IPMTs tends to increase as tumors develop and may be a indicator of the potential invasiveness of the tumor cells.