Peritoneal dissemination is one of the major patterns of postoperative recurrence and a major cause of death in pancreatic ductal adenocarcinoma. To predict the development of postoperative peritoneal dissemination (PPD), correlations between the occurrence of PPD and clinicopathological factors were analyzed in 23 patients with pancreatic ductal carcinoma who underwent tumor resection and were carefully monitored after the operation. Fifteen cases (65.2%) developed PPD, but the other 8 cases (34.8%) did not meet the criteria for a diagnosis of PPD. Location of the tumor in the pancreatic tail or body (p = 0.0041, HR = 10.827, 95% CI = 2.126-55.127) and the presence of extra-tumoral perineural invasion (ETNI) (p = 0.0490, HR = 0.114, 95% CI = 0.013-0.990) were found to have predictive value for the development of PPD. These results suggested that intensive therapy selectively focused on the peritoneum in cases with ETNI, might prevent the development of PPD and reduce the side effects of treatment in cases without ETNI.