The role of interleukin-17 (IL-17) in the tumor microenvironment is controversial. We analyzed the in situ tumor expression of IL-17 in colorectal cancer (CRC), adenoma and non-tumor tissue to explore the possible correlation of IL-17 expression to clinicopathological characteristics, tumor-infiltrating neutrophils (TINs) and survival in CRC.We reviewed the records of 78 consecutive patients diagnosed with CRC. Archival tissues were used. Thirty-six patients with colorectal adenoma were also included. From the 78 CRC patients, we randomly chose 40 cases and collected non-tumor tissue at 10 cm from the edge of the resected tumor. Immunohistochemistry was performed using anti-IL-17 and anti-CD15 (targeting neutrophils) antibody, respectively. Real-time PCR was used to detect IL-17 mRNA in different tissues. Associations between IL-17 expression, clinicopathological parameters and prognosis were evaluated.The level of IL-17 mRNA was higher in CRC than in adenoma and non-tumor tissue (P < 0.05). Positive IL-17 protein expression was observed more frequently in CRC as compared to colorectal adenoma and non-tumor tissue, respectively (P < 0.01). IL-17 expression correlated to well differentiation and early stage CRC. The number of CD15+ neutrophils significantly increased in CRC and positively correlated to the expression of IL-17 (P < 0.05). Both Kaplan–Meier analysis and multivariate Cox regression analysis indicated that patients with positive IL-17 expression showed better overall survival.The association between IL-17 expression and the clinicopathological parameters, as well as the clinical outcome suggests a significant role of IL-17 in CRC. IL-17 is a marker of favorable prognosis.