Abstract Background The objective of this study was to investigate whether the preoperative platelet-lymphocyte (P/L) ratio represents a significant prognostic index in resected pancreatic ductal adenocarcinoma. Methods A total of 110 patients undergoing pancreatoduodenectomy for pancreatic ductal adenocarcinoma over a 10-year period were identified from a prospectively maintained database. Results The preoperative P/L ratio was found to be a more significant prognostic marker ( P < .001) than either the lymphocyte count ( P = .007) or platelet count ( P = .068) on univariate Cox survival analysis. The median overall survival in patients with a P/L ratio of 150 or less (n = 48) was 19.7 months, 13.7 months in those with a P/L ratio of 151 to 300 (n = 43), and 5.8 months in patients with a value of greater than 300 (n = 19) (log-rank, P = .006). The preoperative P/L ratio retained significance on multivariate analysis ( P < .001), along with tumor size ( P = .010) and lymph node ratio ( P = .013). Conclusions The preoperative P/L ratio represents a significant independent prognostic index in patients of resected pancreatic adenocarcinoma.