The prognosis for patients with metastatic gastric cancer is poor. Fewer than 10% of patients with metastatic gastric cancer live beyond 2 years. Chemotherapy is offered with a palliative intent. We report the case of a Western patient with metastatic gastric cancer successfully treated with S-1 plus cisplatin. S-1 was administered orally every 12 h at a dose of 30 mg/m2 (60 mg/m2 daily) for 21 consecutive days, followed by 7 days of recovery. Cisplatin was administered intravenously on day 1, at a dose of 60 mg/m2. The cycles were repeated every 28 days. The patient first received seven cycles of S-1 plus cisplatin; however, cisplatin was discontinued secondary to nephrotoxicity, and S-1 was administered alone for an additional five cycles. The patient achieved a clinical complete response to S-1 plus cisplatin. The complete response has now been maintained for 12 months without any chemotherapy. A total of 28 months have elapsed since the date of registration on the study and the patient currently has no symptoms. This patient exemplifies the strategy of maintenance therapy with S-1 alone and shows a prolonged and excellent response to S-1 and cisplatin.