We investigated the clinical significance of tumour-infiltrating FOXP3-positive regulatory T cells (Tregs) in radically resected (R0) gastric cancer. From a single-institution database, tumors of 110 patients who underwent R0 resection for stage II-III disease were studied for FOXP3-positive Tregs by immunohistochemistry. The observed median number of FOXP3-positive Tregs was used as the cut-point in analyses (<6 versus >or=6 count). Tregs were significantly higher in gastric carcinomas than in normal tissue (P = 0.0001). Tregs count >or=6 was significantly associated with vascular/lymphatic/perineural invasion (VELIPI) in the tumour (P = 0.03). Multivariate analysis showed association between adverse relapse-free survival and grading 3, stage III, VELIPI and Tregs count >or=6 (P = 0.02). Adverse overall survival was associated with grading 3, stage III, VELIPI and Tregs count >or=6 (P = 0.006). FOXP3-positive Tregs may be a novel marker for identifying high-risk gastric cancer patients. Present findings deserve additional investigation as Tregs may also represent an innovative therapeutic target.