BACKGROUND: The recommended treatment for gastric cancer with positive peritoneal cytology (CY1) is primary surgery and S-1 chemotherapy, with 5-year overall survival rates of 24.6%-30.2% reported in previous studies. However, it is unclear whether this strategy is applicable in cases of Type 4 or large Type 3 tumors, which have malignant characteristics and are considered to have different chemosensitivities. METHODS: The present study examined the survival of patients who were diagnosed with gastric cancer with CY1, without any other macroscopic distant metastasis, who underwent primary gastrectomy with D2 or more lymph node resection, achieved curative resection except for CY1-positive, and received S-1 postoperative chemotherapy between 2000 and 2017. Patients were divided into the S group (Type 4 or large Type 3 GC) and C group (common GC types). RESULTS: Among the 352 patients who underwent gastrectomy with CY1, 40 patients were analyzed as the S group and 28 patients as the C group in this study. Both groups were similar in age and ASA-PS, but the S group had more female patients and larger tumors. The median duration of S-1 chemotherapy was 273 days in the S group and 358.5 days in the C group, with similar 1-year continuation rates. The median overall survival of these patients was 24.1 months in the S group and 45.6 months in the C group, with a 5-year survival rate of 23.7% in the S group and 22.0% in the C group. There was no significant difference. Recurrence occurred in 35 patients in the S group and 20 in the C group, with peritoneal metastasis as the most common recurrence site in both groups. CONCLUSIONS: Primary surgery and S-1 chemotherapy could be considered a viable treatment option, even for Type 4 or large Type 3 gastric cancer with CY1.