Nutritional status affects the prognosis of various tumors. The prognostic nutritional index (PNI) is the known predictor of postoperative outcome in resectable pancreatic cancer patients. This study aimed to validate the prognostic value of PNI in all stages of pancreatic cancer. We retrospectively reviewed 499 patients with pancreatic cancer who were diagnosed at Severance Hospital between January 2006 and December 2011. The PNI value was calculated as 10 × serum albumin (g/dL) + 0.005 × total lymphocyte count (/mm3) at initial diagnosis. The median patient age was 62 yr, and 289 were men. The study group comprised resectable disease (n = 121), locally advanced disease (n = 118), and metastatic disease (n = 260). Univariate and multivariate analysis revealed that PNI ≤ 49.5 at initial diagnosis, together with performance status, platelet count, and clinical stage, was significantly associated with overall survival (hazard ratio, 1.562; all P < 0.05). Patients with PNI ≤ 49.5 (n = 208) had shorter median overall survival compared to patients with high PNI (9.8 vs. 14.2 mo; log rank, P < 0.001). In clinical stage subgroup analysis, initial PNI ≤49.5 independently predicted shorter overall survival, especially in resectable and metastatic disease (P = 0.041, P = 0.002, respectively).