Nerve plexus invasion is regarded as one of the most important prognostic factors in invasive ductal carcinoma (IDC) of the pancreas, though nerve plexus invasion has not been evaluated in terms of prognostic impact on the basis of detailed histologic investigation. The purpose of this study was to precisely examine morphologic characteristics of nerve plexus invasion and analyze its prognostic predictive power compared with the well-known prognostic parameters of pancreatic IDCs. The outcome and histologic features of 75 patients with pancreatic IDC in the pancreas head were investigated, and 422 lesions of nerve plexus invasion were evaluated. Tumor cells invading nerve plexus showed a duct-forming differentiated feature and predominantly existed in the perineurium and perineural space. Multivariate analyses revealed that the important prognostic factors, in addition to invasive tumor size and tumor necrosis, were at long distances from nerve plexus invasion to pancreatic capsule and perineural invasion in nerve plexus invasion.