The ACTS-GC trial showed the efficacy of adjuvant treatment with S-1 in patients who had undergone D2 gastrectomy for Stage Ⅱ or Ⅲ(excluding pT1) gastric cancer, classified according to the 13th Japanese Classification of Gastric Carcinoma. We retrospectively analyzed the treatment outcomes of pT1 gastric cancer patients who underwent gastrectomy at our institute to determine the optimal target population for adjuvant treatment among these particular patients. Patients with pT1 gastric cancer who underwent gastrectomy for primary gastric cancer at our institute between 2000 and 2008 without perioperative chemotherapy and mortality were included in the current analysis (n=461). The incidence of lymph node metastasis in M and SM patients were 1.7% (4/240) and 16.7% (37/221), respectively. The 5-year relapse-free survival in M and SM patients was 100% and 96.2%, respectively. On multivariate analysis, the most important risk factor for recurrence in SM patients was 3 or more involved nodes (HR: 6.53, [95%CI: 1.10-31.29], p=0.040). The 5-year relapse-free survival in SM patients with involvement of 3 or more nodes was 66.7% and was comparable with that in stage Ⅱ surgery-only patients in the ACTS-GC trial. Hence, SM patients with 3 or more involved nodes are candidates for effective adjuvant treatment after curative gastrectomy.