The survival of gastric cancer patients with peritoneal dissemination is dismal and surgical intervention is rarely indicated. The usefulness of TS-1, a novel oral anticancer drug, composed of tegafur, gimestat and otastat potassium at a molar ratio of 1:0.4:1, and the role of surgical intervention for this condition was studied. Among gastric cancer patients with peritoneal dissemination, 18 treated during September 1999 to March 2001, and 16 before March 1999, were classified into the TS-1 group and control group, respectively, and survival was compared. TS-1 was administered orally twice daily, at a dose of 80 mg/m2/day, for 28 days followed by 14 days without treatment. This cycle was repeated. There was no difference in clinicopathologic factors, including surgical intervention, between the two groups. Eleven patients of the control group had chemotherapy using fluoropyrimidine. Grade 3-4 adverse reactions caused by TS-1 occurred in 1 patient. Survival was better in the TS-1 group than control group (p=0.0008), with median survival of 257 vs. 118 days. The median discharged period of patients of the TS-1 group with a performance status 0-2 on the Zubor scale was 211 days. TS-1 was effective to prolong the survival of gastric cancer patients with peritoneal dissemination. In this series of cases, surgical intervention to establish the route of oral administration was essential for this treatment.