In cases with advanced/recurrent gastric cancer undergoing single therapy with TS-1, we retrospectively discussed the antitumor effects and adverse events and considered the clinical utility of TS-1. The subjects consisted of 131 cases with advanced/recurrent gastric cancer who received one or more courses of therapy with TS-1 alone between July 1999 and August 2003. We carried out 4-week administration of 80-120 mg/day of TS-1 according to body surface area, followed by a 2-week discontinuation, then repeated administration which adjusting the dosage according to the incidence of side effects, and discussed the antitumor effects and adverse events. The response rate in all cases was 21% and the median survival time (MST) was 343 days, or 25.3% and 265 days if limited to unresectable and recurrent cases. The response rates were 38.2% for unresectable cases, 16.3% for recurrent cases and 14.6% for curability C cases, and the MSTs were 250 days, 276 days and 419 days, respectively. The response rates in terms of whether or not patients had received chemotherapy were 11.6% for those who had received chemotherapy and 40.0% for those who had not, and the MSTs were 239 days and 325 days, respectively. Thus, both were significantly better in patients who had not received chemotherapy. The response rates for patients who had not received chemical therapy by target organs were favorable on the order of 50% for stomach and 33% for liver metastasis, and the MSTs were on the order of 474 days for peritoneum, 39 1 days for liver metastasis and 326 days for lymph nodes. There were 10 cases of long-term survival of 600 days or longer, but not in unresectable cases, and the target organs in many of the cases were the peritoneum and lymph nodes. Adverse reactions were observed in 34.4% of all cases and those of grade 3 or more in 9.4%, all of which were improved only by discontinuation of the drug. It was again confirmed that single therapy with TS-1 for advanced/recurrent gastric cancer is an excellent therapy providing both high antitumor effects and safety.