Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive malignancies, with an overall 5-year survival rate of less than 5%. Invasive tumor growth and early metastasis are two important reasons for this dismal prognosis. Osteopontin (OPN) is a secretory protein with a variety of functions, for example in cell adhesion and migration, inflammatory reaction and apoptosis. In this study the functional role of OPN in human pancreatic cancer and its potential use as a disease marker were analyzed. By real time quantitative PCR, there was a 2.2-fold and 1.6-fold increase of OPN mRNA in pancreatic cancers (n = 23) and chronic pancreatitis samples (n = 22), respectively, compared to normal pancreatic tissues (n = 20). Immunohistochemical analysis demonstrated OPN staining in 60% of the primary pancreatic tumors and in 72% of the lymph node and liver metastases. ELISA analysis of serum samples obtained from pancreatic cancer patients (n = 70), chronic pancreatitis patients (n = 12), and healthy donors (n = 20) showed a 1.6-fold increase in OPN serum levels in patients with tumors and a 1.9-fold increase in patients with chronic pancreatitis. Recombinant human OPN significantly increased the invasiveness of pancreatic cancer cells, without having any impact on cell proliferation. In addition, down regulation of OPN by specific siRNA molecules decreased pancreatic cancer cell invasion. In conclusion, OPN serum levels in pancreatic cancer and chronic pancreatitis patients are not significantly different, thereby restricting its role as a prognostic or follow-up marker. Our results do suggest, however, that blockade of OPN might be useful as a therapeutic approach to inhibit invasion and metastasis of pancreatic cancer cells.