Purpose: To evaluate the survival benefit of adjuvant chemotherapy after curative resection in serosa-positive gastric cancer patients, a multicenter phase III clinical trial was conducted by 13 participating centers in Japan. Methods: From January 1993 to March 1998, 268 patients were randomized to either adjuvant chemotherapy (135 pts) or surgery alone (133 pts). The chemotherapy comprised intraperitoneal cisplatin 70 mg/m2 before closing the abdomen, and after surgery intravenous cisplatin 70 mg/m2 (day 14) and 5-fluorouracil (5-FU) 700 mg/m2 daily (day 14-16), and oral FU (UFT) 267 mg/m2 daily from 4 weeks after surgery for the next 12 months. The primary endpoint was overall survival. Relapse-free survival and the site of recurrence were secondary endpoints.