Background: Although a causal relationship between inflammation and innate immunity of cancer is more widely accepted today, many of the precise cellular mechanisms mediating this relationship remain unclear. Th17 cells, which produce the proinflammatory cytokine IL-17, have been recognized as one of the key factors in regulation of inflammatory bowel disease and rheumatoid arthritis. Methods: This study demonstrated that, in patients with digestive system cancers including 7 patients with esophageal, 14 with gastric, 20 with colorectal, 5 with hepatocellular, 7 with cholangiocellular, and 7 with pancreatic carcinomas, IL-17 production was correlated with MDSC level and with markers for nutritional impairment, immune suppression and chronic inflammation. Results: IL-17 production was significantly higher in patients with all types of digestive cancer than in normal volunteers. In addition, IL-17 production levels were significantly correlated with neutrophil counts and the neutrophil/lymphocyte ratio, and significantly inversely correlated with cell mediated immune response indicators (lymphocyte PHA-blastogenesis and IL-12 production) and patients’ nutritional status (prealbumin levels). Circulating MDSC levels were significantly correlated with IL-17 production. Conclusions: These results suggest that, in human gastrointestinal cancers, chronic inflammation involving IL-17 may be an important mechanism for disease progression through enhancement of immune suppression or cachexia. Controlling activation of Th17 cells may prove to be a valuable strategy for treatment of patients with gastrointestinal cancer.