Nucleus accumbens-associated protein 1 (NAC1) is overexpressed in various carcinomas including ovarian, cervical, breast, and pancreatic carcinomas. High expression of NAC1 is considered to have adverse effects on prognosis through negative regulation of growth arrest and DNA-damage–inducible 45-γ interacting protein 1 (GADD45GIP1) in ovarian and cervical carcinomas. In the present study, the expression of NAC1 in pancreatic ductal adenocarcinoma (PDA) was measured using immunohistochemistry and computer-assisted image analysis in order to investigate its correlation with various clinicopathological parameters and prognosis. Patients with low-NAC1 PDA had worse overall survival (P = 0.0010) and a shorter disease-free survival (P = 0.0036) than patients with high-NAC1 PDA. This was a clinical effect opposite to that reported in ovarian and cervical carcinomas. Furthermore, knockdown of NAC1 in pancreatic carcinoma cell lines did not increase expression of the GADD45GIP1 protein. These results indicate that the gene(s) regulated by NAC1 vary depending on the types of carcinoma or originating tissue, and that low expression of NAC1 predicts poor prognosis for patients with PDA.