Neutrophils are conspicuous components of gastric cancer (GC) tumors, increasing with tumor progression and poor patient survival. However, the phenotype, regulation, function and clinical relevance of neutrophils in human GC are presently unknown. We used flow cytometry analyses to examine levels and phenotype of neutrophils in samples from 50 patients with GC. Kaplan-Meier plots for patient survival were performed using the log-rank test, and multivariate analysis of prognostic factors for patient survival was performed using the Cox proportional hazards model. Neutrophils were isolated, stimulated and/or cultured for regulation and function assays. We found that GC patients showed a significantly higher neutrophil infiltration in tumors, and that neutrophil infiltration was positively associated with tumor progression but negatively correlated with patient survival. Most tumor-infiltrating neutrophils showed an activated CD54