This randomised multicentre phase II study was conducted to investigate the activity and safety of two oral fluoropyrimidines, capecitabine or S-1, in elderly patients with advanced gastric cancer (AGC). Elderly (>or=65 years) chemo-naive patients with AGC were randomly assigned to receive capecitabine 1250 mg m(-2) two times daily on days 1-14 every 3 weeks or S-1 40-60 mg two times daily according to body surface area on days 1-28 every 6 weeks. Ninety-six patients were enrolled and 91 patients were randomised to capecitabine (N=46) or S-1 (N=45). Overall response rate, the primary end point, was 27.2% (95% CI, 14.1-40.4, 12 of 44 assessable patients) with capecitabine and 28.9% (95% CI, 15.6-42.1, 13 of 45) with S-1. Median times to progression and overall survival in the capecitabine arm (4.7 and 9.5 months, respectively) were similar to those in the S-1 arm (4.2 and 8.2 months, respectively). The incidence of grade 3-4 granulocytopenia was 6.8% with capecitabine and 4.8% with S-1. Grade 3-4 nonhaematologic toxicities were: asthenia (9.1% with capecitabine vs 7.1% with S-1), anorexia (6.8 vs 9.5%), diarrhoea (2.3 vs 0%), and hand-foot syndrome (6.8 vs 0%). Both capecitabine and S-1 monotherapies were active and tolerable as first-line treatment for elderly patients with AGC.