Interleukin-11 (IL-11) affects inflammation, motility, and invasion in cancer. Here, we investigated the clinical significance of plasma IL-11 (IL-11p) levels in patients with pancreatic cancer. We enrolled 44 patients with pathologically confirmed diagnoses of pancreatic cancer into this study (median age at diagnosis, 68 years; range, 42-86 years), along with 30 age- and sex-matched healthy controls and 3 patients with pancreatitis complicated with pancreatic cysts and 15 patients with early pancreatitis. Median baseline IL-11p levels of patients with pancreatic cancer were significantly higher than that of the healthy controls (P < 0.001), as were those of the 15 patients with early pancreatitis. IL-11p levels presented high diagnostic accuracy for pancreatic cancer (area under the curve (AUC), 0.901; sensitivity, 97.7%; specificity, 70.0%). Age, sex, lesion site, disease stage, serum dehydrogenase, alkaline phosphatase, γ-glutamyltransferase, and white blood cells, platelets, and hemoglobin levels did not correlate with IL-11p concentrations (P>0.05), but patients with distant metastases had lower median IL-11p values than did patients without distant metastases (P=0.043). Patients with IL-11p higher than the median level (43.2 pg/mL) had better prognoses than those with lower values (P=0.004), particularly as IL-11p concentration increased to ≥ 50 pg/mL (P=0.001). IL-11p concentration correlated with overall survival (≥ median IL-11p, 10 months; <median IL-11p, 4.0 months; P=0.004). In conclusion, IL-11p has diagnostic, predictive, and prognostic applications for patients with pancreatic cancer.